What I want to achieve:
Define a function that can be used to pipe input, such as echo input | my_function
This function modifies every inputted line, e.g., it adds indentation at the beginning.
This function can be reused twice and in that case does its modification (double indent) twice, e.g. echo input | my_function | my_function results in \t\tinput.
This function does not wait for whole input to be supplied, it can print out the line directly without seeing all input.
As for my test, please see the following script:
#!/usr/bin/env bash
main() {
echo 'first:'
echo 'once' | tab_indent_to_right
echo 'twice' | tab_indent_to_right | tab_indent_to_right
{
echo 'wait 2 sec'
sleep 2
echo 'wait 2 sec'
sleep 2
echo 'waited'
} | tab_indent_to_right
}
tab_indent_to_right() {
# while read -r line; do echo $'\t'"$line"; done # 🔴 double indent not working
# awk -v prefix='\t' '{print prefix $0}' # 🔴 buffer not working
# sed 's/^/\t/' # 🔴 buffer not working
# xargs -I {} echo $'\t{}' # 🔴 double indent not working
# xargs -L1 echo $'\t' # 🔴 double indent not working
}
main
Each line in tab_indent_to_right is my failed attempt to solve the problem. They have two different problems, either:
Double indent is not working e.g., tab_indent_to_right | tab_indent_to_right
Or, the lines are not being flushed/printed directly but instead being buffered. In other words, the function waits for all sleeps and prints out everything at once, instead of printing the lines as they come.
How can I create this function so both double calls gives me the modification I want and also the script does not wait for complete execution of the piped shell?
I suggest to set IFS to nothing to keep spaces/tabs.
tab_indent_to_right() {
while IFS= read -r line; do echo $'\t'"$line"; done
}
In recentish versions of awk, you can use the fflush() function to force it to send output lines immediately:
awk -v prefix='\t' '{print prefix $0; fflush()}'
Also, depending on the version of sed you have, you may be able to add either the -u flag (for "unbuffered"; GNU sed supports this) or the -l flag ("line buffered"; bsd sed supports this). If you have some other version of sed... check its man page to see if it has a similar option.
BTW, the bsd version of sed doesn't support \t for tab; but if you use $'s/^/\t/', bash will convert \t to tab before passing it to sed. This works with both versions of sed, but not with shells that don't support ANSI quoting mode (i.e. dash).
I'm using ssh to connect to a remote machine and read a log file there. From that log file, based on some tokens, I extract specific logs and store it in a variable. Every log is in new line in the log file and the data can contain any character including white space.
array=("$(egrep "UserComments/propagateBundle-2013-10-19--04:42:13|UserComments/propagateBundle-2013-10-19--04:38:36|UserComments/propagateBundle-2013-10-19--04:34:24" <path>/propagateBundle.log)")
echo ${array[0]}
echo "$array"
First echo prints complete output in one line separated by white space while the other prints outputs in new line. Problem, is, I'm not able to save this output as an array. I tried this:
newArray=("$array")
max=${#newArray[#]}
echo $max
But echoing 'max' yields '1' on the screen. How can I save the output in an array? I also tried using
IFS=\`\n`
but could not get the data in an array.
EDIT
I used the solution given by Anubhav and it worked like charm. Now I faced a second issue. Since my data contains white spaces, so the array broke at white spaces and wrongly contained the one comments as multiple arrays. So, I used
IFS=\`\n`
and also used a $ symbol before backticks. Although this solves my problem, I still get an exception in the logs:
test.sh: line 11: n: command not found
Any suggestions?
Don't put quotes in the command substitution:
array=( $(egrep "UserComments/propagateBundle-2013-10-19--04:42:13|UserComments/propagateBundle-2013-10-19--04:38:36|UserComments/propagateBundle-2013-10-19--04:34:24" <path>/propagateBundle.log) )
With quotes as in your code whole output is treated as single string in the array.
I've used IFS=('\n') otherwise all "n" chars disappears from results and sort command doesn't work properly. See bellow, it is a customized llq output.
#!/bin/bash
IFS=('\n')
raw=(`llq -f %id %o %gu %gl %st %BS %c`)
echo
echo ${raw[*]} | grep "step(s)"
echo
echo ${raw[*]} | grep "Step"
echo ${raw[*]} | grep "\---*"
echo ${raw[*]} | grep "bgp-fn*" | sort -k5 -r
echo ${raw[*]} | grep "\---*"
echo ${raw[*]} | grep "Step"
echo
echo ${raw[*]} | grep "step(s)"
echo
I'm trying to find a solution to a problem analog to this one:
#command_A
A_output_Line_1
A_output_Line_2
A_output_Line_3
#command_B
B_output_Line_1
B_output_Line_2
Now I need to compare A_output_Line_2 and B_output_Line_1 and echo "Correct" if they are equal and "Not Correct" otherwise.
I guess the easiest way to do this is to copy a line of output in some variable and then after executing the two commands, simply compare the variables and echo something.
This I need to implement in a bash script and any information on how to get certain line of output stored in a variable would help me put the pieces together.
Also, it would be cool if anyone can tell me not only how to copy/store a line, but probably just a word or sequence like : line 1, bytes 4-12, stored like string in a variable.
I am not a complete beginner but also not anywhere near advanced linux bash user. Thanks to any help in advance and sorry for bad english!
An easier way might be to use diff, no?
Something like:
command_A > command_A.output
command_B > command_B.output
diff command_A.output command_B.output
This will work for comparing multiple strings.
But, since you want to know about single lines (and words in the lines) here are some pointers:
# first line of output of command_A
command_A | head -n 1
The -n 1 option says only to use the first line (default is 10 I think)
# second line of output of command_A
command_A | head -n 2 | tail -n 1
that will take the first two lines of the output of command_A and then the last of those two lines. Happy times :)
You can now store this information in a variable:
export output_A=`command_A | head -n 2 | tail -n 1`
export output_B=`command_B | head -n 1`
And then compare it:
if [ "$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]}" = "${array_b[0]}" ]; then
echo "CORRECT"
else
echo "INCORRECT"
fi
Normally when one wants to look at specific output lines from running something, one can do something like:
./a.out | grep IHaveThisString
but what if IHaveThisString is something which changes every time so you need to first run it, watch the output to catch what IHaveThisString is on that particular run, and then grep it out? I can just dump to file and later grep but is it possible to do something like background it and then bring it to foreground and bringing it back but now piped to some grep? Something akin to:
./a.out
Ctrl-Z
fg | grep NowIKnowThisString
just wondering..
No, it is only in your screen buffer if you didn't save it in some other way.
Short form: You can do this, but you need to know that you need to do it ahead-of-time; it's not something that can be put into place interactively after-the-fact.
Write your script to determine what the string is. We'd need a more detailed example of the output format to give a better example of usage, but here's one for the trivial case where the entire first line is the filter target:
run_my_command | { read string_to_filter_for; fgrep -e "$string_to_filter_for" }
Replace the read string_to_filter_for with as many commands as necessary to read enough input to determine what the target string is; this could be a loop if necessary.
For instance, let's say that the output contains the following:
Session id: foobar
and thereafter, you want to grep for lines containing foobar.
...then you can pipe through the following script:
re='Session id: (.*)'
while read; do
if [[ $REPLY =~ $re ]] ; then
target=${BASH_REMATCH[1]}
break
else
# if you want to print the preamble; leave this out otherwise
printf '%s\n' "$REPLY"
fi
done
[[ $target ]] && grep -F -e "$target"
If you want to manually specify the filter target, this can be done by having the loop check for a file being created with filter contents, and using that when starting up grep afterwards.
That is a little bit strange what you need, but you can do it tis way:
you must go into script session first;
then you use shell how usually;
then you start and interrupt you program;
then run grep over typescript file.
Example:
$ script
$ ./a.out
Ctrl-Z
$ fg
$ grep NowIKnowThisString typescript
You could use a stream editor such as sed instead of grep. Here's an example of what I mean:
$ cat list
Name to look for: Mike
Dora 1
John 2
Mike 3
Helen 4
Here we find the name to look for in the fist line and want to grep for it. Now piping the command to sed:
$ cat list | sed -ne '1{s/Name to look for: //;h}' \
> -e ':r;n;G;/^.*\(.\+\).*\n\1$/P;s/\n.*//;br'
Mike 3
Note: sed itself can take file as a parameter, but you're not working with text files, so that's how you'd use it.
Of course, you'd need to modify the command for your case.
Trying to debug an issue with a server and my only log file is a 20GB log file (with no timestamps even! Why do people use System.out.println() as logging? In production?!)
Using grep, I've found an area of the file that I'd like to take a look at, line 347340107.
Other than doing something like
head -<$LINENUM + 10> filename | tail -20
... which would require head to read through the first 347 million lines of the log file, is there a quick and easy command that would dump lines 347340100 - 347340200 (for example) to the console?
update I totally forgot that grep can print the context around a match ... this works well. Thanks!
I found two other solutions if you know the line number but nothing else (no grep possible):
Assuming you need lines 20 to 40,
sed -n '20,40p;41q' file_name
or
awk 'FNR>=20 && FNR<=40' file_name
When using sed it is more efficient to quit processing after having printed the last line than continue processing until the end of the file. This is especially important in the case of large files and printing lines at the beginning. In order to do so, the sed command above introduces the instruction 41q in order to stop processing after line 41 because in the example we are interested in lines 20-40 only. You will need to change the 41 to whatever the last line you are interested in is, plus one.
# print line number 52
sed -n '52p' # method 1
sed '52!d' # method 2
sed '52q;d' # method 3, efficient on large files
method 3 efficient on large files
fastest way to display specific lines
with GNU-grep you could just say
grep --context=10 ...
No there isn't, files are not line-addressable.
There is no constant-time way to find the start of line n in a text file. You must stream through the file and count newlines.
Use the simplest/fastest tool you have to do the job. To me, using head makes much more sense than grep, since the latter is way more complicated. I'm not saying "grep is slow", it really isn't, but I would be surprised if it's faster than head for this case. That'd be a bug in head, basically.
What about:
tail -n +347340107 filename | head -n 100
I didn't test it, but I think that would work.
I prefer just going into less and
typing 50% to goto halfway the file,
43210G to go to line 43210
:43210 to do the same
and stuff like that.
Even better: hit v to start editing (in vim, of course!), at that location. Now, note that vim has the same key bindings!
You can use the ex command, a standard Unix editor (part of Vim now), e.g.
display a single line (e.g. 2nd one):
ex +2p -scq file.txt
corresponding sed syntax: sed -n '2p' file.txt
range of lines (e.g. 2-5 lines):
ex +2,5p -scq file.txt
sed syntax: sed -n '2,5p' file.txt
from the given line till the end (e.g. 5th to the end of the file):
ex +5,p -scq file.txt
sed syntax: sed -n '2,$p' file.txt
multiple line ranges (e.g. 2-4 and 6-8 lines):
ex +2,4p +6,8p -scq file.txt
sed syntax: sed -n '2,4p;6,8p' file.txt
Above commands can be tested with the following test file:
seq 1 20 > file.txt
Explanation:
+ or -c followed by the command - execute the (vi/vim) command after file has been read,
-s - silent mode, also uses current terminal as a default output,
q followed by -c is the command to quit editor (add ! to do force quit, e.g. -scq!).
I'd first split the file into few smaller ones like this
$ split --lines=50000 /path/to/large/file /path/to/output/file/prefix
and then grep on the resulting files.
If your line number is 100 to read
head -100 filename | tail -1
Get ack
Ubuntu/Debian install:
$ sudo apt-get install ack-grep
Then run:
$ ack --lines=$START-$END filename
Example:
$ ack --lines=10-20 filename
From $ man ack:
--lines=NUM
Only print line NUM of each file. Multiple lines can be given with multiple --lines options or as a comma separated list (--lines=3,5,7). --lines=4-7 also works.
The lines are always output in ascending order, no matter the order given on the command line.
sed will need to read the data too to count the lines.
The only way a shortcut would be possible would there to be context/order in the file to operate on. For example if there were log lines prepended with a fixed width time/date etc.
you could use the look unix utility to binary search through the files for particular dates/times
Use
x=`cat -n <file> | grep <match> | awk '{print $1}'`
Here you will get the line number where the match occurred.
Now you can use the following command to print 100 lines
awk -v var="$x" 'NR>=var && NR<=var+100{print}' <file>
or you can use "sed" as well
sed -n "${x},${x+100}p" <file>
With sed -e '1,N d; M q' you'll print lines N+1 through M. This is probably a bit better then grep -C as it doesn't try to match lines to a pattern.
Building on Sklivvz' answer, here's a nice function one can put in a .bash_aliases file. It is efficient on huge files when printing stuff from the front of the file.
function middle()
{
startidx=$1
len=$2
endidx=$(($startidx+$len))
filename=$3
awk "FNR>=${startidx} && FNR<=${endidx} { print NR\" \"\$0 }; FNR>${endidx} { print \"END HERE\"; exit }" $filename
}
To display a line from a <textfile> by its <line#>, just do this:
perl -wne 'print if $. == <line#>' <textfile>
If you want a more powerful way to show a range of lines with regular expressions -- I won't say why grep is a bad idea for doing this, it should be fairly obvious -- this simple expression will show you your range in a single pass which is what you want when dealing with ~20GB text files:
perl -wne 'print if m/<regex1>/ .. m/<regex2>/' <filename>
(tip: if your regex has / in it, use something like m!<regex>! instead)
This would print out <filename> starting with the line that matches <regex1> up until (and including) the line that matches <regex2>.
It doesn't take a wizard to see how a few tweaks can make it even more powerful.
Last thing: perl, since it is a mature language, has many hidden enhancements to favor speed and performance. With this in mind, it makes it the obvious choice for such an operation since it was originally developed for handling large log files, text, databases, etc.
print line 5
sed -n '5p' file.txt
sed '5q' file.txt
print everything else than line 5
`sed '5d' file.txt
and my creation using google
#!/bin/bash
#removeline.sh
#remove deleting it comes move line xD
usage() { # Function: Print a help message.
echo "Usage: $0 -l LINENUMBER -i INPUTFILE [ -o OUTPUTFILE ]"
echo "line is removed from INPUTFILE"
echo "line is appended to OUTPUTFILE"
}
exit_abnormal() { # Function: Exit with error.
usage
exit 1
}
while getopts l:i:o:b flag
do
case "${flag}" in
l) line=${OPTARG};;
i) input=${OPTARG};;
o) output=${OPTARG};;
esac
done
if [ -f tmp ]; then
echo "Temp file:tmp exist. delete it yourself :)"
exit
fi
if [ -f "$input" ]; then
re_isanum='^[0-9]+$'
if ! [[ $line =~ $re_isanum ]] ; then
echo "Error: LINENUMBER must be a positive, whole number."
exit 1
elif [ $line -eq "0" ]; then
echo "Error: LINENUMBER must be greater than zero."
exit_abnormal
fi
if [ ! -z $output ]; then
sed -n "${line}p" $input >> $output
fi
if [ ! -z $input ]; then
# remove this sed command and this comes move line to other file
sed "${line}d" $input > tmp && cp tmp $input
fi
fi
if [ -f tmp ]; then
rm tmp
fi
You could try this command:
egrep -n "*" <filename> | egrep "<line number>"
Easy with perl! If you want to get line 1, 3 and 5 from a file, say /etc/passwd:
perl -e 'while(<>){if(++$l~~[1,3,5]){print}}' < /etc/passwd
I am surprised only one other answer (by Ramana Reddy) suggested to add line numbers to the output. The following searches for the required line number and colours the output.
file=FILE
lineno=LINENO
wb="107"; bf="30;1"; rb="101"; yb="103"
cat -n ${file} | { GREP_COLORS="se=${wb};${bf}:cx=${wb};${bf}:ms=${rb};${bf}:sl=${yb};${bf}" grep --color -C 10 "^[[:space:]]\\+${lineno}[[:space:]]"; }