I am trying to create a wordlist consisting of the same password followed by a 4-digit numeric pin. The pin goes through every possible combination of 10,000 variations. The desired output should be like this:
UoMYTrfrBFHyQXmg6gzctqAwOmw1IohZ 1111
UoMYTrfrBFHyQXmg6gzctqAwOmw1IohZ 1112
UoMYTrfrBFHyQXmg6gzctqAwOmw1IohZ 1113
and so on.
I created a shell script that almost get this, but awk doesn't seem to like having a variable passed through it, and seems to just print out every combination when called. This is the shell script:
#!/bin/bash
# Creates 10,000 lines of the bandit24pass and every possible combination
# Of 4 digits pin
USER="UoMYTrfrBFHyQXmg6gzctqAwOmw1IohZ"
PASS=$( echo {1,2,3,4,5,6,7,8,9}{1,2,3,4,5,6,7,8,9}{1,2,3,4,5,6,7,8,9}{1,2,3,4,5,6,7,8,9} | awk '{print $I}' )
for I in {1..10000};
do
echo "$USER $PASS"
done
I though $I would translate to $1 for the first run of the loop, and increment upwards through each iteration. Any help would be greatly appreciated.
I though $I would translate to $1 for the first run of the loop, and increment upwards through each iteration.
No, command substitutions are expanded once; like, when you do foo=$(echo), foo is an empty line, not a reference to echo.
This whole task could be achieved by a single call to printf btw.
printf 'UoMYTrfrBFHyQXmg6gzctqAwOmw1IohZ %s\n' {1111..9999}
Tyr this
$echo $user
UoMYTrfrBFHyQXmg6gzctqAwOmw1IohZ
$for i in {1000..9999}; do echo $user $i; done;
I am working on a script. I have a file called test.txt whose contents are as follows:
a. parent = 192.168.1.2
b. child1 = 192.168.1.21
c. child2 = 192.154.1.2
I need to store the values in three different variables called parent, child1and child2 as follows and then my script will use these values:
parent = 192.168.1.2
child1= 192.168.1.21
child2= 192.154.1.2
How can I do that using sed or awk? I know there is a way to extract substrings using awk function substr but my particular requirement is tostore them in variables as mentioned above. Thanks
Try this if you're using bash:
$ declare $(awk '{print $2"="$4}' file)
$ echo "$parent"
192.168.1.2
If the file contained white space in the values you want to init the variables with then you'd just have to set IFS to a newline before invoking declare, e.g. (simplified the input file to highlight the important part of white space on the right of the = signs):
$ cat file
parent=192.168.1.2 is first
child1=192.168.1.21 comes after it
child2=and then theres 192.154.1.2
$ IFS=$'\n'; declare $(awk -F'=' '{print $1"="$2}' file)
$ echo "$parent"
192.168.1.2 is first
$ echo "$child1"
192.168.1.21 comes after it
Ed Morton's answer is the way to go for the specific problem at hand - elegant and concise.
Update: Ed has since updated his answer to also provide a solution that correctly deals with variable value values with embedded spaces - the original lack of which prompted this answer.
His solution is superior to this one - more concise and more efficient (the only caveat is that you may have to restore the previous $IFS value afterward).
This solution may still be of interest if you need to process variable definitions one by one, e.g., in order to transform variable values based on other shell functions or variables before assigning them.
The following uses bash with process substitution on a simplified problem to process variable definitions one by one:
#!/usr/bin/env bash
while read -r name val; do # read a name-value pair
# Assign the value after applying a transformation to it; e.g.:
# 'value of' -> 'value:'
declare $name="${val/ of /: }" # `declare "$name=${val/ of /: }"` would work too.
done < <(awk -F= '{print $1, $2}' <<<$'v1=value of v1\nv2= value of v2')
echo "v1=[$v1], v2=[$v2]" # -> 'v1=[value: v1], v2=[value: v2]'
awk's output lines are read line by line, split into name and value, and declared as shell variables individually.
Since read, which trims by whitespace, is only given 2 variable names to read into, the 2nd one receives everything from the 2nd token _through the end of the line, thus preserving interior whitespace (and, as written, will trim leading and trailing whitespace in the process).
Note that declare normally does not require a variable reference on the RHS of the assignment (the value) to be double-quoted (e.g. a=$b; though it never hurts). In this particular case, however - seemingly because the LHS (the name) is also a variable reference - the double quotes are needed.
I also got it done finally . Thanks everyone for helping.
counter=0
while read line
do
declare $(echo $line | awk '{print $2"="$4}')
#echo "$parent"
if [ $counter = 0 ]
then
parent=$(echo $parent)
fi
if [ $counter = 1 ]
then
child1=$(echo $child)
else
child2=$(echo $child)
fi
counter=$((counter+1))
done < "/etc/cluster_info.txt"
eval "$( sed 's/..//;s/ *//g' YourFile )"
just a sed equivalent to Ed solution and with an eval instead of declare.
I'm trying to find a solution to a problem analog to this one:
#command_A
A_output_Line_1
A_output_Line_2
A_output_Line_3
#command_B
B_output_Line_1
B_output_Line_2
Now I need to compare A_output_Line_2 and B_output_Line_1 and echo "Correct" if they are equal and "Not Correct" otherwise.
I guess the easiest way to do this is to copy a line of output in some variable and then after executing the two commands, simply compare the variables and echo something.
This I need to implement in a bash script and any information on how to get certain line of output stored in a variable would help me put the pieces together.
Also, it would be cool if anyone can tell me not only how to copy/store a line, but probably just a word or sequence like : line 1, bytes 4-12, stored like string in a variable.
I am not a complete beginner but also not anywhere near advanced linux bash user. Thanks to any help in advance and sorry for bad english!
An easier way might be to use diff, no?
Something like:
command_A > command_A.output
command_B > command_B.output
diff command_A.output command_B.output
This will work for comparing multiple strings.
But, since you want to know about single lines (and words in the lines) here are some pointers:
# first line of output of command_A
command_A | head -n 1
The -n 1 option says only to use the first line (default is 10 I think)
# second line of output of command_A
command_A | head -n 2 | tail -n 1
that will take the first two lines of the output of command_A and then the last of those two lines. Happy times :)
You can now store this information in a variable:
export output_A=`command_A | head -n 2 | tail -n 1`
export output_B=`command_B | head -n 1`
And then compare it:
if [ "$output_A" == "$output_B" ]; then echo 'Correct'; else echo 'Not Correct'; fi
To just get parts of a string, try looking into cut or (for more powerful stuff) sed and awk.
Also, just learing a good general purpose scripting language like python or ruby (even perl) can go a long way with this kind of problem.
Use the IFS (internal field separator) to separate on newlines and store the outputs in an array.
#!/bin/bash
IFS='
'
array_a=( $(./a.sh) )
array_b=( $(./b.sh) )
if [ "${array_a[1]}" = "${array_b[0]}" ]; then
echo "CORRECT"
else
echo "INCORRECT"
fi
I wanted to write a short shell script, which removes specified pages from a pdf. Maybe I'm doing that in a bit convoluted manner, but that is what I came up with so far:
#!/bin/bash
#This is a script to remove a specified page from a specified pdf.
set verbose
s="A1-$(($2-1))"
if [ n -ge 3 ]; then
for i in 2..$#
do
s+=A$(($($i)+1))-$(($($(($i+1)))-1))
done
fi
pdftk A="$1" cat $s A$(($($#)+1))-end output output.pdf
I know it's quite convoluted code and if you know about the working of pdftk, I would appreciate a hint to make it easier, but for now I just need to know how to substitute a variable into a variable name. E.g. if
i=2
a2=3
echo $a($i)
gave me 3, that would be great, but it doesn't. How do I achieve this?
bash allows indirect parameter expansion:
$ i=2
$ a2=3
$ var="a$i" # a2
$ echo "${!var}"
3
What you really seem to want, though, is an array:
$ a=([2]=3) # Or simply a[2]=3
$ i=2
$ echo "${a[i]}"
3
(This is really a stop-gap answer, as there is almost certainly a much simpler answer to your question that doesn't involve this type of indirect parameter manipulation.)
I think this much simpler script that will do what you want:
#!/bin/bash
inputfile=$1
shift
ranges=() from=1
for pageToOmit in "$#"; do
ranges+=( "A$from-$(( pageToOmit - 1))" )
from=$(( pageToOmit + 1 ))
done
ranges+=( "$from-end" )
pdftk A="$inputfile" cat "${ranges[#]}" output output.pdf
Using eval:
i=2
a2=3
eval echo \$a$i
eval b=\$a$i
echo $b
After reading the Bash man pages and with respect to this post, I am still having trouble understanding what exactly the eval command does and which would be its typical uses.
For example, if we do:
$ set -- one two three # Sets $1 $2 $3
$ echo $1
one
$ n=1
$ echo ${$n} ## First attempt to echo $1 using brackets fails
bash: ${$n}: bad substitution
$ echo $($n) ## Second attempt to echo $1 using parentheses fails
bash: 1: command not found
$ eval echo \${$n} ## Third attempt to echo $1 using 'eval' succeeds
one
What exactly is happening here and how do the dollar sign and the backslash tie into the problem?
eval takes a string as its argument, and evaluates it as if you'd typed that string on a command line. (If you pass several arguments, they are first joined with spaces between them.)
${$n} is a syntax error in bash. Inside the braces, you can only have a variable name, with some possible prefix and suffixes, but you can't have arbitrary bash syntax and in particular you can't use variable expansion. There is a way of saying “the value of the variable whose name is in this variable”, though:
echo ${!n}
one
$(…) runs the command specified inside the parentheses in a subshell (i.e. in a separate process that inherits all settings such as variable values from the current shell), and gathers its output. So echo $($n) runs $n as a shell command, and displays its output. Since $n evaluates to 1, $($n) attempts to run the command 1, which does not exist.
eval echo \${$n} runs the parameters passed to eval. After expansion, the parameters are echo and ${1}. So eval echo \${$n} runs the command echo ${1}.
Note that most of the time, you must use double quotes around variable substitutions and command substitutions (i.e. anytime there's a $): "$foo", "$(foo)". Always put double quotes around variable and command substitutions, unless you know you need to leave them off. Without the double quotes, the shell performs field splitting (i.e. it splits value of the variable or the output from the command into separate words) and then treats each word as a wildcard pattern. For example:
$ ls
file1 file2 otherfile
$ set -- 'f* *'
$ echo "$1"
f* *
$ echo $1
file1 file2 file1 file2 otherfile
$ n=1
$ eval echo \${$n}
file1 file2 file1 file2 otherfile
$eval echo \"\${$n}\"
f* *
$ echo "${!n}"
f* *
eval is not used very often. In some shells, the most common use is to obtain the value of a variable whose name is not known until runtime. In bash, this is not necessary thanks to the ${!VAR} syntax. eval is still useful when you need to construct a longer command containing operators, reserved words, etc.
Simply think of eval as "evaluating your expression one additional time before execution"
eval echo \${$n} becomes echo $1 after the first round of evaluation. Three changes to notice:
The \$ became $ (The backslash is needed, otherwise it tries to evaluate ${$n}, which means a variable named {$n}, which is not allowed)
$n was evaluated to 1
The eval disappeared
In the second round, it is basically echo $1 which can be directly executed.
So eval <some command> will first evaluate <some command> (by evaluate here I mean substitute variables, replace escaped characters with the correct ones etc.), and then run the resultant expression once again.
eval is used when you want to dynamically create variables, or to read outputs from programs specifically designed to be read like this. See Eval command and security issues for examples. The link also contains some typical ways in which eval is used, and the risks associated with it.
In my experience, a "typical" use of eval is for running commands that generate shell commands to set environment variables.
Perhaps you have a system that uses a collection of environment variables, and you have a script or program that determines which ones should be set and their values. Whenever you run a script or program, it runs in a forked process, so anything it does directly to environment variables is lost when it exits. But that script or program can send the export commands to standard output.
Without eval, you would need to redirect standard output to a temporary file, source the temporary file, and then delete it. With eval, you can just:
eval "$(script-or-program)"
Note the quotes are important. Take this (contrived) example:
# activate.sh
echo 'I got activated!'
# test.py
print("export foo=bar/baz/womp")
print(". activate.sh")
$ eval $(python test.py)
bash: export: `.': not a valid identifier
bash: export: `activate.sh': not a valid identifier
$ eval "$(python test.py)"
I got activated!
The eval statement tells the shell to take eval’s arguments as commands and run them through the command-line. It is useful in a situation like below:
In your script if you are defining a command into a variable and later on you want to use that command then you should use eval:
a="ls | more"
$a
Output:
bash: command not found: ls | more
The above command didn't work as ls tried to list file with name pipe (|) and more. But these files are not there:
eval $a
Output:
file.txt
mailids
remote_cmd.sh
sample.txt
tmp
Update: Some people say one should -never- use eval. I disagree. I think the risk arises when corrupt input can be passed to eval. However there are many common situations where that is not a risk, and therefore it is worth knowing how to use eval in any case. This stackoverflow answer explains the risks of eval and alternatives to eval. Ultimately it is up to the user to determine if/when eval is safe and efficient to use.
The bash eval statement allows you to execute lines of code calculated or acquired, by your bash script.
Perhaps the most straightforward example would be a bash program that opens another bash script as a text file, reads each line of text, and uses eval to execute them in order. That's essentially the same behavior as the bash source statement, which is what one would use, unless it was necessary to perform some kind of transformation (e.g. filtering or substitution) on the content of the imported script.
I rarely have needed eval, but I have found it useful to read or write variables whose names were contained in strings assigned to other variables. For example, to perform actions on sets of variables, while keeping the code footprint small and avoiding redundancy.
eval is conceptually simple. However, the strict syntax of the bash language, and the bash interpreter's parsing order can be nuanced and make eval appear cryptic and difficult to use or understand. Here are the essentials:
The argument passed to eval is a string expression that is calculated at runtime. eval will execute the final parsed result of its argument as an actual line of code in your script.
Syntax and parsing order are stringent. If the result isn't an executable line of bash code, in scope of your script, the program will crash on the eval statement as it tries to execute garbage.
When testing you can replace the eval statement with echo and look at what is displayed. If it is legitimate code in the current context, running it through eval will work.
The following examples may help clarify how eval works...
Example 1:
eval statement in front of 'normal' code is a NOP
$ eval a=b
$ eval echo $a
b
In the above example, the first eval statements has no purpose and can be eliminated. eval is pointless in the first line because there is no dynamic aspect to the code, i.e. it already parsed into the final lines of bash code, thus it would be identical as a normal statement of code in the bash script. The 2nd eval is pointless too, because, although there is a parsing step converting $a to its literal string equivalent, there is no indirection (e.g. no referencing via string value of an actual bash noun or bash-held script variable), so it would behave identically as a line of code without the eval prefix.
Example 2:
Perform var assignment using var names passed as string values.
$ key="mykey"
$ val="myval"
$ eval $key=$val
$ echo $mykey
myval
If you were to echo $key=$val, the output would be:
mykey=myval
That, being the final result of string parsing, is what will be executed by eval, hence the result of the echo statement at the end...
Example 3:
Adding more indirection to Example 2
$ keyA="keyB"
$ valA="valB"
$ keyB="that"
$ valB="amazing"
$ eval eval \$$keyA=\$$valA
$ echo $that
amazing
The above is a bit more complicated than the previous example, relying more heavily on the parsing-order and peculiarities of bash. The eval line would roughly get parsed internally in the following order (note the following statements are pseudocode, not real code, just to attempt to show how the statement would get broken down into steps internally to arrive at the final result).
eval eval \$$keyA=\$$valA # substitution of $keyA and $valA by interpreter
eval eval \$keyB=\$valB # convert '$' + name-strings to real vars by eval
eval $keyB=$valB # substitution of $keyB and $valB by interpreter
eval that=amazing # execute string literal 'that=amazing' by eval
If the assumed parsing order doesn't explain what eval is doing enough, the third example may describe the parsing in more detail to help clarify what is going on.
Example 4:
Discover whether vars, whose names are contained in strings, themselves contain string values.
a="User-provided"
b="Another user-provided optional value"
c=""
myvarname_a="a"
myvarname_b="b"
myvarname_c="c"
for varname in "myvarname_a" "myvarname_b" "myvarname_c"; do
eval varval=\$$varname
if [ -z "$varval" ]; then
read -p "$varname? " $varname
fi
done
In the first iteration:
varname="myvarname_a"
Bash parses the argument to eval, and eval sees literally this at runtime:
eval varval=\$$myvarname_a
The following pseudocode attempts to illustrate how bash interprets the above line of real code, to arrive at the final value executed by eval. (the following lines descriptive, not exact bash code):
1. eval varval="\$" + "$varname" # This substitution resolved in eval statement
2. .................. "$myvarname_a" # $myvarname_a previously resolved by for-loop
3. .................. "a" # ... to this value
4. eval "varval=$a" # This requires one more parsing step
5. eval varval="User-provided" # Final result of parsing (eval executes this)
Once all the parsing is done, the result is what is executed, and its effect is obvious, demonstrating there is nothing particularly mysterious about eval itself, and the complexity is in the parsing of its argument.
varval="User-provided"
The remaining code in the example above simply tests to see if the value assigned to $varval is null, and, if so, prompts the user to provide a value.
I originally intentionally never learned how to use eval, because most people will recommend to stay away from it like the plague. However I recently discovered a use case that made me facepalm for not recognizing it sooner.
If you have cron jobs that you want to run interactively to test, you might view the contents of the file with cat, and copy and paste the cron job to run it. Unfortunately, this involves touching the mouse, which is a sin in my book.
Lets say you have a cron job at /etc/cron.d/repeatme with the contents:
*/10 * * * * root program arg1 arg2
You cant execute this as a script with all the junk in front of it, but we can use cut to get rid of all the junk, wrap it in a subshell, and execute the string with eval
eval $( cut -d ' ' -f 6- /etc/cron.d/repeatme)
The cut command only prints out the 6th field of the file, delimited by spaces. Eval then executes that command.
I used a cron job here as an example, but the concept is to format text from stdout, and then evaluate that text.
The use of eval in this case is not insecure, because we know exactly what we will be evaluating before hand.
I've recently had to use eval to force multiple brace expansions to be evaluated in the order I needed. Bash does multiple brace expansions from left to right, so
xargs -I_ cat _/{11..15}/{8..5}.jpg
expands to
xargs -I_ cat _/11/8.jpg _/11/7.jpg _/11/6.jpg _/11/5.jpg _/12/8.jpg _/12/7.jpg _/12/6.jpg _/12/5.jpg _/13/8.jpg _/13/7.jpg _/13/6.jpg _/13/5.jpg _/14/8.jpg _/14/7.jpg _/14/6.jpg _/14/5.jpg _/15/8.jpg _/15/7.jpg _/15/6.jpg _/15/5.jpg
but I needed the second brace expansion done first, yielding
xargs -I_ cat _/11/8.jpg _/12/8.jpg _/13/8.jpg _/14/8.jpg _/15/8.jpg _/11/7.jpg _/12/7.jpg _/13/7.jpg _/14/7.jpg _/15/7.jpg _/11/6.jpg _/12/6.jpg _/13/6.jpg _/14/6.jpg _/15/6.jpg _/11/5.jpg _/12/5.jpg _/13/5.jpg _/14/5.jpg _/15/5.jpg
The best I could come up with to do that was
xargs -I_ cat $(eval echo _/'{11..15}'/{8..5}.jpg)
This works because the single quotes protect the first set of braces from expansion during the parsing of the eval command line, leaving them to be expanded by the subshell invoked by eval.
There may be some cunning scheme involving nested brace expansions that allows this to happen in one step, but if there is I'm too old and stupid to see it.
You asked about typical uses.
One common complaint about shell scripting is that you (allegedly) can't pass by reference to get values back out of functions.
But actually, via "eval", you can pass by reference. The callee can pass back a list of variable assignments to be evaluated by the caller. It is pass by reference because the caller can allowed to specify the name(s) of the result variable(s) - see example below. Error results can be passed back standard names like errno and errstr.
Here is an example of passing by reference in bash:
#!/bin/bash
isint()
{
re='^[-]?[0-9]+$'
[[ $1 =~ $re ]]
}
#args 1: name of result variable, 2: first addend, 3: second addend
iadd()
{
if isint ${2} && isint ${3} ; then
echo "$1=$((${2}+${3}));errno=0"
return 0
else
echo "errstr=\"Error: non-integer argument to iadd $*\" ; errno=329"
return 1
fi
}
var=1
echo "[1] var=$var"
eval $(iadd var A B)
if [[ $errno -ne 0 ]]; then
echo "errstr=$errstr"
echo "errno=$errno"
fi
echo "[2] var=$var (unchanged after error)"
eval $(iadd var $var 1)
if [[ $errno -ne 0 ]]; then
echo "errstr=$errstr"
echo "errno=$errno"
fi
echo "[3] var=$var (successfully changed)"
The output looks like this:
[1] var=1
errstr=Error: non-integer argument to iadd var A B
errno=329
[2] var=1 (unchanged after error)
[3] var=2 (successfully changed)
There is almost unlimited band width in that text output! And there are more possibilities if the multiple output lines are used: e.g., the first line could be used for variable assignments, the second for continuous 'stream of thought', but that's beyond the scope of this post.
In the question:
who | grep $(tty | sed s:/dev/::)
outputs errors claiming that files a and tty do not exist. I understood this to mean that tty is not being interpreted before execution of grep, but instead that bash passed tty as a parameter to grep, which interpreted it as a file name.
There is also a situation of nested redirection, which should be handled by matched parentheses which should specify a child process, but bash is primitively a word separator, creating parameters to be sent to a program, therefore parentheses are not matched first, but interpreted as seen.
I got specific with grep, and specified the file as a parameter instead of using a pipe. I also simplified the base command, passing output from a command as a file, so that i/o piping would not be nested:
grep $(tty | sed s:/dev/::) <(who)
works well.
who | grep $(echo pts/3)
is not really desired, but eliminates the nested pipe and also works well.
In conclusion, bash does not seem to like nested pipping. It is important to understand that bash is not a new-wave program written in a recursive manner. Instead, bash is an old 1,2,3 program, which has been appended with features. For purposes of assuring backward compatibility, the initial manner of interpretation has never been modified. If bash was rewritten to first match parentheses, how many bugs would be introduced into how many bash programs? Many programmers love to be cryptic.
As clearlight has said, "(p)erhaps the most straightforward example would be a bash program that opens another bash script as a text file, reads each line of text, and uses eval to execute them in order". I'm no expert, but the textbook I'm currently reading (Shell-Programmierung by Jürgen Wolf) points to one particular use of this that I think would be a valuable addition to the set of potential use cases collected here.
For debugging purposes, you may want to go through your script line by line (pressing Enter for each step). You could use eval to execute every line by trapping the DEBUG signal (which I think is sent after every line):
trap 'printf "$LINENO :-> " ; read line ; eval $line' DEBUG
I like the "evaluating your expression one additional time before execution" answer, and would like to clarify with another example.
var="\"par1 par2\""
echo $var # prints nicely "par1 par2"
function cntpars() {
echo " > Count: $#"
echo " > Pars : $*"
echo " > par1 : $1"
echo " > par2 : $2"
if [[ $# = 1 && $1 = "par1 par2" ]]; then
echo " > PASS"
else
echo " > FAIL"
return 1
fi
}
# Option 1: Will Pass
echo "eval \"cntpars \$var\""
eval "cntpars $var"
# Option 2: Will Fail, with curious results
echo "cntpars \$var"
cntpars $var
The curious results in option 2 are that we would have passed two parameters as follows:
First parameter: "par1
Second parameter: par2"
How is that for counter intuitive? The additional eval will fix that.
It was adapted from another answer on How can I reference a file for variables using Bash?