I need to create a script that uses an 'if' command that checks whether there is exactly one argument. If there is more than one argument, I need it to echo “Usage: give exactly 1 argument, the string to be looked for” and then exit immediately.
Welcome to Stackoverflow.
This should do the trick:
if [ "$#" -gt 1 ]; then
echo "Usage: give exactly 1 argument, the string to be looked for"
exit 0
else
echo the expected processing happens in this section of this code
fi
Related
I wrote bash script, in which I included some logging, to see what is going on in each step of exectuion.
Now, I can split those logs in debuggin info and user info (that something has completed, etc.). So I'd like to have some flag parameter, like --verbose, which I saw in some other bash functions to enable full logging and usage was like:
some_function --verbose
or
some_function -v
I call it flag parameters and don't know what's the right name, thus I can't find anything useful.
How to define such parameters for bash script?
Case suits better for this
while [[ "$#" ]]; do
case "$1" in
-v|--verbose) verbose="true";;
esac
shift
done
Same can be done in function, but note that in this case it'll process parameters passed to function some_function -v.
some_function () {
while [[ "$#" ]]; do
case "$1" in
-v|--verbose) verbose="true";;
esac
shift
done
}
Then somewhere in script you can check if verbose is set
[[ "$verbose" ]] && echo "verbose mode" || echo "silent mode"
For now, I used workaround and take it as normal positional parameter (as $n). To be exact, I have list of four parameters, so I collect this flag like this:
verbose=$4
if [ ! "$verbose" == "--verbose" ]; then
verbose=""
fi
So, if parameter is not matching a flag, then I leave it empty and if I want to use it, I just compare it against empty string.
There's one big disadvantage for me though: it has to be at 4th position in parameters list.
I have a small script that I am working on. This is only the second script that I have made using bash script.
Basically what I am wanting this script to do is take the users input and fire a command based on that choice.
As you can see the user first enters the host address of the instance they are going to ssh into and ultimately tail logs on. There are a couple things that I am not understanding.
If / Then / Else / Elif - The concept seems simple enough but perhaps how these should be used eludes me.
When I run my script through a bash parser, the parser comes back with the following message:
Line 2:
if [ "$mainmenuinput" = "1" ]; then
^-- SC2154: mainmenuinput is referenced but not assigned.
mainmenu() {
if [ "$mainmenuinput" = "1" ]; then
ssh "$customerurl" tail -f /data/jirastudio/jira/j2ee_*/log/main/current
elif [ "$mainmenuinput" = "2" ]; then
ssh "$customerurl" tail -f /data/jirastudio/confluence/j2ee_*/log/main/current
elif [ "$mainmenuinput" = "3" ]; then
ssh "$customerurl" tail -f /data/jirastudio/horde/service/log/main/current
elif [ "$mainmenuinput" = "4" ]; then
ssh "$customerurl" tail -f /data/jirastudio/apache/logs/access_log
fi
}
printf "\nEnter the customers host URL:\n"
read -r customerurl
printf "Press 1 for JIRA\n"
printf "Press 2 for Confluence\n"
printf "Press 3 for Horde\n"
printf "Press 4 for Apache Access\n"
printf "Press 5 for Apache Error\n"
read -p -r "Make your choice:" "$mainmenuinput"
Looking up the SC2154 entry I found that it means this:
ShellCheck has noticed that you reference a variable that is not assigned. Double check that the variable is indeed assigned, and that the name is not misspelled.
I am a little confused on what that means. If someone can explain that, I would greatly appreciate it.
As it stands, when I run the script, it pauses to wait for the user to enter the host address. The user hits ENTER and the script then presents them with the menu to have them choose which log they want to tail. The menu looks a little odd:
Press 1 for JIRA
Press 2 for Confluence
Press 3 for Horde
Press 4 for Apache Access
Press 5 for Apache Error
-r
Im not sure why the -r is showing up at the end of the menu. When a selection is made, the script ends and outputs this:
./tail_logs.sh: line 23: read:Make your choice:': not a valid identifier`
Any help with this would be appreciated or if anything a push in the right direction. I love figuring this stuff out but sometimes, its helpful to get shoved at least in the general direction of the error/resolution.
Thanks
EDIT 1
Ok, I updated my script with your suggestions. It seemed to still balk at a few things. For example:
(mainmenu "$customerurl" "$mainmenuinput")
Using ShellCheck I got back this:
Line 1:
(mainmenu "$customerurl" "$mainmenuinput") {
^-- SC2154: customerurl is referenced but not assigned.
^-- SC2154: mainmenuinput is referenced but not assigned.
^-- SC1070: Parsing stopped here. Mismatched keywords or invalid parentheses?
If I write this out like:
mainmenu() { then it does not complain. Also, if I run the script with it typed out as per the suggested way, I get an error about `syntax error near unexpected token '{'
The current code looks like this:
#!/bin/sh
mainmenu() {
echo "$1"
echo "$2"
if [ "$2" = "1" ]; then
ssh "$1" tail -f "/data/jirastudio/jira/j2ee_*/log/main/current"
elif [ "$2" = "2" ]; then
ssh "$1" tail -f "/data/jirastudio/confluence/j2ee_*/log/main/current"
elif [ "$2" = "3" ]; then
ssh "$1" tail -f "/data/jirastudio/horde/service/log/main/current"
elif [ "$2" = "4" ]; then
ssh "$1" tail -f "/data/jirastudio/apache/logs/access_log"
elif [ "$2" > 4 || < 1 ]; then
echo "Uh uh uh, you didnt say the magic word! The number you picked isnt in the list. Pick again."
fi
}
echo
echo "Enter the customers host address:"
read -r customerurl
echo "Press 1 for JIRA"
echo "Press 2 for Confluence"
echo "Press 3 for Horde"
echo "Press 4 for Apache Access"
echo "Press 5 for Apache Error"
read -r -p "Pick a number: " mainmenuinput
I get no errors when running this. But when I make a selection, the script ends and does not output the tail command at all. Also, Im not sure if I am validating user input outside of 1-4 correctly with the last elif statement although if I change this to else I get an error when I run the script.
I think my issue is in the first part of the function?
mainmenu() {
echo "$1"
echo "$2"
Without having $hostAddress and mainMenuInput does the script not know what should be assigned to $1 and $2 or does it automatically assign the first thing typed in to these variables?
The main problems are with the read command at the end. First, whatever immediately follows the -p option is used as a prompt string; in this case, the next argument is "-r", so it prints that as a prompt. You clearly want "Make your choice:" to be the prompt, so that must go immediately after -p (i.e. use either read -r -p "Make your choice:" ... or read -p "Make your choice:" -r ...). Second, when you use $mainmenuinput, it replaces that with the current value of mainmenuinput. In the shell, you use $variable to get the value of a variable, not to set it. With both of these problems corrected, the last command becomes:
read -p "Make your choice:" -r mainmenuinput
There's also another important thing: after reading the users' input, you need to actually call the mainmenu function. So just add mainmenu as the last line.
As for the if ... then ... elif ... structure, yours looks fine; I'm not sure what the question is. Although personally I'd add an else clause that printed an error that the option was not valid.
I do have some stylistic/best practice recommendations, though:
It's best to pass information to functions in the form of arguments, rather than global variables. That is, rather than using customerurl and mainmenuinput directly in the function, pass them as arguments (mainmenu "$customerurl" "$mainmenuinput"), then reference those arguments ("$1" and "$2") inside the functions. This doesn't matter much in a small script like this, but having clear distinctions between the variables used by different parts of a program makes things much easier to keep straight in larger programs.
In shell scripts, printf is the best way to do complex things like printing lines without a linefeed at the end, or translating escape characters... but if you're just doing a standard print-a-line-with-a-linefeed-at-the-end, echo is simpler. Thus, I'd replace the various printf "something\n" commands with echo "something", and printf "\nEnter the customers host URL:\n" with:
echo
echo "Enter the customers host URL:"
In the command
ssh "$customerurl" tail -f /data/jirastudio/jira/j2ee_*/log/main/current
(or ssh "$1" ... if you follow my recommendation about arguments instead of global variables), the wildcard (*) will be expanded on the local computer before being handed to ssh and passed to the remote computer to be executed. It'd be best to quote that argument to prevent that:
ssh "$customerurl" tail -f "/data/jirastudio/jira/j2ee_*/log/main/current"
Note that the quotes will be removed before it's passed to ssh and then to the remote computer, so they will not prevent the wildcard from being expanded on the remote computer.
The thing you're calling a URL isn't actually a URL; URLs are things like "https://stackoverflow.com/questions". They start with a protocol (or "scheme") like "http" or "ftp", then "://", then a server name, then "/", etc. ssh just takes a raw server name (optionally with a username, in the form user#server).
Update, based on EDIT 1: I wasn't clear on how to call the function; your definition (using mainmenu() { ...) is correct, but having defined the function you then need to actually run the function. Do to this, change the end of the script to something like this:
...
echo "Press 5 for Apache Error"
read -r -p "Pick a number: " mainmenuinput
mainmenu "$customerurl" "$mainmenuinput"
This will run the function, with the first argument ($1) set to "$customerurl", and second argument ($2) set to "$mainmenuinput".
There's also a problem with the elif clause you added in the function. The shell's syntax for test expressions is really really weird (mostly for historical reasons). Also, there are three common variants, the original [ ... ] (which is actually a command) which has the weirdest syntax, bash's [[ ... ]] variant (much cleaner syntax, but not available available in generic POSIX shells), and (( ... )) (cleaner syntax, math- rather than string-oriented, not portable). See BashFAQ #31 for details.
For what you're trying to do, any of these would work:
elif [ "$2" -gt 4 -o "$2" -lt 1 ]; then
# [ ... ] doesn't use || or &&, and uses -lt etc for numeric comparisons.
# < and > do string comparisons, which are ... different. And you'd
# need to quote them to keep them from being mistaken for redirects.
# Also, you need to specify the "$2" explicitly for each comparison.
elif [[ "$2" -gt 4 || "$2" -lt 1 ]]; then
# [[ ... ]] uses || and &&, but still uses -lt etc for numeric comparisons.
# < and > still do string comparisons, but don't need to be quoted
elif (( $2 > 4 || $2 < 1 )); then
# All numeric here, so < and > work
But there's still a problem, since the user might have entered something that isn't a number at all (just pressed return, typed "wibble", etc.), and in all of these cases numeric comparison will fail. Solution: skip the test, and use else instead of elif:
...
elif [ "$2" = "4" ]; then
ssh "$1" tail -f "/data/jirastudio/apache/logs/access_log"
else
echo "Uh uh uh, you didnt say the magic word! The number you picked isnt in the list. Pick again."
fi
}
... that way, if any of the previous conditions aren't met for any reason at all, it'll print the error message.
In a book I'm reading the below line
ls "$1" 2>/dev/null | grep "$1" 2>/dev/null 1>&2
when written in a script - by the book it says "The command is executed to check whether the file passed as the command line argument exists. The standard error is redirected to /dev/null (the unix black hole), and standard output is redirected to standard error by using 1>&2. Thus, the command does not produce any output or error message; its only puprose is to set the command returns status value $?."
But running the code:
if [ $? -eq 0 ]
would I not know it otherwise, I have tried without the cmd at beginning and with it as well with having no impact on the results. I'm sure the author would have written for some purpose. I cannot just figure what?
This looks like a very bad book, giving code that noone sane would ever write to poorly illustrate concepts that are generally used in completely different ways in shell scripts.
The line:
ls "$1" 2>/dev/null | grep "$1" 2>/dev/null 1>&2
is as described -- it has no visible effect other than setting the return code. Is your question about what this does in detail to get a return code or something else?
The line:
if [ $? -eq 0 ]
is an incomplete fragment that checks the return code of the previous command. It's incomplete as there is no then or fi, without which the shell will reject it as a syntax error and not do anything (if you type the above at a prompt, you'll get the secondary prompt, telling you the shell is waiting for more input to get a complete command). So without more code there's no apparent effect. Something more complete like:
if [ $? -eq 0 ]; then echo YES; else echo NO; fi
would output YES or NO based on that return code.
A more sensible way of doing the 6 lines starting with the ls would be:
if [ ! -e "$1" ]; then
echo "$1: not found"
exit 1
fi
As to what the ls line actually does, it runs ls (list files) with the name in $1 as an argument, then uses grep to search that listing for the same filename.
So if the file does not exist, ls gives an error and outputs nothing, so the grep fails (setting $? to 1). If the filename exists and is not a directory, the grep will succeed (setting $? to 0). Finally, if the filename exists and is a directory, it will search the contents of that directory, looking for any file or subdirectory with the same name as a substring -- which is probably just a bug. In addition, if $1 is a string beginning with -, it will do something fairly useless and unpredictable.
Overall, a prime example of a shell script that should never be written -- any student that turned in such a monstrosity should get an immediate F.
I'm confused about why can't get the script's parameter count in a function, could anybody help me? thanks in advance:)
test.sh
#!/bin/bash
check(){
echo $#
if [ $# -lt 2 ]; then
echo "Argument missing"
exit 1
fi
}
echo $#
check
Run:
./test.sh aa bb
output:
2
0
Functions have their own local copies of the argument variables, including $#. They are related to the arguments of the function, and the equivalents at the script level are shadowed. If you want to get the script's argument variables then you will need to either store them somewhere else first or pass them to the function.
check "$#"
I have the following bash script file callee.sh which is being called from another script file caller.sh.
The callee.sh is as follows:
if [ $1 -eq 1 ];
then
echo inside $1
source ~/MYPROGRAMSRC/standAloneWordCount.sh $2
#echo "inside standalone branch"
#echo $1
elif [ $1 -eq 2 ];
then
#echo "inside distributed branch"
#echo $1
else
echo invalid option for first argument-\n Options:\n "distributed"\n or\n "standalone"\n
fi
As most people might be able to tell, this is a script I use to decide whether to run hadoop in distributed or standAlone mode depending on the arguments.
This script is called from caller.sh as follows
source callee.sh $2 $counterGlobal
where $2 is a number either 1 or 2 and $counterGlobal is some integer.
My problem is that the if condition in callee.sh never evaluates to True and hence my script standAloneWordCount.sh which I call from within callee.sh is never called. I am running with bash shell and have tried many variants of the if statement like:
if [ $(($1 == 1 )) ] -- (1)
In an echo statement just above the line -- (1) , the expression $(($1 == 1)) evaluates to 1 so I am baffled as to why I am unable to satisfy the if condition.
Also I keep getting the error where it says:
syntax error near unexpected token `else'
if anyone could help me out with these two errors, it would be much appreciated. As I've run out of ideas.
Thanks in advance!
have tried many variants of the if statement like:
if [ $(($1 == 1 )) ]
You should instead be saying:
if (($1 == 1)); then
...
fi
Regarding the Syntax error near unexpected tokenelse'`, it's not because of any code that you've shown above. It seems to originate from some other portion of your script.
If you're using bash, try using double square brackets:
if [[ $1 -eq 1 ]]; then
echo "inside 1"
fi
As for the syntax error, you need quotes around your text (which also means escaping the existing quotes or use single quotes):
echo -e "invalid option for first argument-\n Options:\n \"distributed\"\n or\n \"standalone\"\n"
The -e flag is there to let bash know you want the \n to evaluate to a newline.