I need a bash script to invoke itself (actually in a different context, inside Docker container) and I'm using a bash -c command to do so. However, I'm struggling with how to pass on all command line variables, even after reading lots of related questions here. This is an example script:
#!/bin/bash
# If not in the right context, invoke script in right context and exit
if [ -z ${NESTED+x} ]; then
NESTED=true bash -c "./test.sh $#"
exit
fi
echo "$1"
echo "$2"
echo "$3"
If I save this as test.sh and call it with ./test.sh 1 2 "3 4" I'd want to see those arguments echo'ed, but only the first one is output.
If I use set -x it shows bash inserts some unexpected quoting so the call becomes NESTED=true bash -c './test2.sh 1' 2 3 4. That explains the output but I haven't been able to figure out the right way to do this.
bash -c should not be used as it cannot handle "3 4" easily:
#!/bin/bash
# If not in the right context, invoke script in right context and exit
if [ -z ${NESTED+x} ]; then
NESTED=true ./test.sh "$#"
exit
fi
echo "$1"
echo "$2"
echo "$3"
Related
This is my sample Bash Script example.sh:
#!/bin/bash
# Reading arguments and mapping to respective variables
while [ $# -gt 0 ]; do
if [[ $1 == *"--"* ]]; then
v="${1/--/}"
declare $v
fi
shift
done
# Printing command line arguments through the mapped variables
echo ${arg1}
echo ${arg2}
Now if in terminal I run the bash script as follows:
$ bash ./example.sh "--arg1=value1" "--arg2=value2"
I get the correct output like:
value1
value2
Perfect! Meaning I was able to use the values passed to the arguments --arg1 and --arg2 using the variables ${arg1} and ${arg2} inside the bash script.
I am happy with this solution for now as it serves my purpose, but, anyone can suggest any better solution to use named command line arguments in bash scripts?
You can just use environment variables:
#!/bin/bash
echo "$arg1"
echo "$arg2"
No parsing needed. From the command line:
$ arg1=foo arg2=bar ./example.sh
foo
bar
There's even a shell option to let you put the assignments anywhere, not just before the command:
$ set -k
$ ./example.sh arg1=hello arg2=world
hello
world
I'm getting started with bash scripting and made this little script following along a short guide but for some reason when I run the script with sh myscript I get
myscript: 5: myscript: 0: not found running on ubuntu 12.04
here is my script below I should at least see the echo message if no args are set:
#!/bin/bash
#will do something
name=$1
username=$2
if (( $# == 0 ))
then
echo "##############################"
echo "myscript [arg1] [arg2]"
echo "arg1 is your name"
echo "and arg2 is your username"
fi
var1="Your name is ${name} and your username is ${username}"
`echo ${var1} > yourname.txt`
`echo ${var1} > yourname.txt`
Get rid of the backticks.
echo ${var1} > yourname.txt
...for some reason when I run the script with sh myscript...
Don't run it that way. Make the script executable and run it directly
chmod +x myscript
./script
(or run with bash myscript explicitly).
It looks like that expression will work in bash but not in sh. As others pointed out change it to executable, make sure your shebang line is using bash and run it like this:
./myscript
If you want to run it with sh then it is complaining about line 5. Change it to this and it will work in /bin/sh.
if [ $# -ne 0 ]
Check out the man page for test.
Also you don't need the backticks on this line:
echo ${var1} > yourname.txt
Here I am again. Today I wrote a little script that is supposed to start an application silently in my debian env.
Easy as
silent "npm search 1234556"
This works but not at all.
As you can see, I commented the section where I have some troubles.
This line:
$($cmdLine) &
doesn't hide application output but this one
$($1 >/dev/null 2>/dev/null) &
works perfectly. What am I missing? Many thanks.
#!/bin/sh
# Daniele Brugnara
# October, 2013
# Silently exec a command line passed as argument
errorsRedirect=""
if [ -z "$1" ]; then
echo "Please, don't joke me..."
exit 1
fi
cmdLine="$1 >/dev/null"
# if passed a second parameter, errors will be hidden
if [ -n "$2" ]; then
cmdLine="$cmdLine 2>/dev/null"
fi
# not working
$($cmdLine) &
# works perfectly
#$($1 >/dev/null 2>/dev/null) &
With the use of evil eval following script will work:
#!/bin/sh
# Silently exec a command line passed as argument
errorsRedirect=""
if [ -z "$1" ]; then
echo "Please, don't joke me..."
exit 1
fi
cmdLine="$1 >/dev/null"
# if passed a second parameter, errors will be hidden
if [ -n "$2" ]; then
cmdLine="$cmdLine 2>&1"
fi
eval "$cmdLine &"
Rather than building up a command with redirection tacked on the end, you can incrementally apply it:
#!/bin/sh
if [ -z "$1" ]; then
exit
fi
exec >/dev/null
if [ -n "$2" ]; then
exec 2>&1
fi
exec $1
This first redirects stdout of the shell script to /dev/null. If the second argument is given, it redirects stderr of the shell script too. Then it runs the command which will inherit stdout and stderr from the script.
I removed the ampersand (&) since being silent has nothing to do with running in the background. You can add it back (and remove the exec on the last line) if it is what you want.
I added exec at the end as it is slightly more efficient. Since it is the end of the shell script, there is nothing left to do, so you may as well be done with it, hence exec.
& means that you're doing sort of multitask whereas
1 >/dev/null 2>/dev/null
means that you redirect the output to a sort of garbage and that's why you don't see anything.
Furthermore cmdLine="$1 >/dev/null" is incorrect, you should use ' instead of " :
cmdLine='$1 >/dev/null'
you can build your command line in a var and run a bash with it in background:
bash -c "$cmdLine"&
Note that it might be useful to store the output (out/err) of the program, instead of trow them in null.
In addition, why do you need errorsRedirect??
You can even add a wait at the end, just to be safe...if you want...
#!/bin/sh
# Daniele Brugnara
# October, 2013
# Silently exec a command line passed as argument
[ ! $1 ] && echo "Please, don't joke me..." && exit 1
cmdLine="$1>/dev/null"
# if passed a second parameter, errors will be hidden
[ $2 ] && cmdLine+=" 2>/dev/null"
# not working
echo "Running \"$cmdLine\""
bash -c "$cmdLine" &
wait
$ cat test.sh
set -eu
echo "`wc -l < $DNE`"
echo should not get here
$ /bin/bash test.sh
test.sh: line 2: DNE: unbound variable
should not get here
I'm running bash version 4.1.2. Is there a way to make sure all such usage of unbound variables in subshells cause the script to exit without having to modify each call involving a subshell?
The better solution to ensure variable sanitisation
#!/usr/bin/env bash
set -eu
if [[ ${1-} ]]; then
DNE=$1
else
echo "ERROR: Please enter a valid filename" 1>&2
exit 1
fi
By putting a hyphen in to the variable name inside curly braces like this allows bash to sanely handle the variable being undefined. I also highly recommend looking at the Google shell style guide, it's a great reference https://google.github.io/styleguide/shell.xml
[[ -z ${variable-} ]] \
&& echo "ERROR: Unset variable \${variable}" \
&& exit 1 \
|| echo "INFO: Using variable (${variable})"
Use a temporary variable so as to let test.sh process know about the failure of wc. You can change it to:
#!/bin/bash
set -eu
out=$(wc -l < $DNE)
echo $out
echo should not get here
Now, you won't see the should not get here if wc fails.
Suppose a shell script (/bin/sh or /bin/bash) contained several commands. How can I cleanly make the script terminate if any of the commands has a failing exit status? Obviously, one can use if blocks and/or callbacks, but is there a cleaner, more concise way? Using && is not really an option either, because the commands can be long, or the script could have non-trivial things like loops and conditionals.
With standard sh and bash, you can
set -e
It will
$ help set
...
-e Exit immediately if a command exits with a non-zero status.
It also works (from what I could gather) with zsh. It also should work for any Bourne shell descendant.
With csh/tcsh, you have to launch your script with #!/bin/csh -e
May be you could use:
$ <any_command> || exit 1
You can check $? to see what the most recent exit code is..
e.g
#!/bin/sh
# A Tidier approach
check_errs()
{
# Function. Parameter 1 is the return code
# Para. 2 is text to display on failure.
if [ "${1}" -ne "0" ]; then
echo "ERROR # ${1} : ${2}"
# as a bonus, make our script exit with the right error code.
exit ${1}
fi
}
### main script starts here ###
grep "^${1}:" /etc/passwd > /dev/null 2>&1
check_errs $? "User ${1} not found in /etc/passwd"
USERNAME=`grep "^${1}:" /etc/passwd|cut -d":" -f1`
check_errs $? "Cut returned an error"
echo "USERNAME: $USERNAME"
check_errs $? "echo returned an error - very strange!"