Pretty new to shell scripting. I am trying to do the following:
#!/bin/bash
unzip myfile.zip
#do stuff if unzip successful
I know that I can just chain the commands together in with && but there is quite a chunk, it would not be terribly maintainable.
You can use the exit status of the command explicitly in the test:
if ! unzip myfile.zip &> /dev/null; then
# handle error
fi
/dev/null is the bit-bucket, you can redirect anything you like to it and it will get thrown away. 2>&1 tells it to direct stderr to the stdout.You can use $?. It returns:
- 0 if the command was successfully executed.
- !0 if the command was unsuccessful.
So you can do
#!/bin/bash
unzip myfile.zip
if [ "$?" -eq 0 ]; then
#do stuff on unzip successful
fi
$ cat a
hello
$ echo $?
0
$ cat b
cat: b: No such file or directory
$ echo $?
1
$? contains the exit status of the most recently executed command. That depends on the command and, in the case of the unzip command there are 17 possible return values. The information about exit status is usually found in the man page for the command.
[ $? ] && echo "error!" will echo error even if $? is 0. It tests whether the string is empty, not whether the string is nonzero.
[ "$?" -eq 0 ] is the way to go?if unzip myfile.zip; then would be even better, but yes, if you're going to do the comparison after-the-fact, your above comment is an improvement on what's in the answer now.The variable $? contains the exit status of the previous command. A successful exit status for (most) commands is (usually) 0, so just check for that...
#!/bin/bash
unzip myfile.zip
if [ $? == 0 ]
then
# Do something
fi
grep returns 0 if it has found a pattern and 1 if it hasn't. The exit status of 1 indicates that it has executed successfully, but hasn't found the pattern. Add the -q option and it returns 0 even if there's an error. In contrast, find returns 0 even if it hasn't found its pattern.if unzip myfile.zip; then : "Do something"; fi? Decoupling through $? just adds potential for bugs -- add an echo between your unzip and your if, and suddenly $? reflects the exit status of the logging statement, not the unzip command.If you want the shell to check the result of the executed commands and stop interpretation when something returns non-zero value you can add set -e which means Exit immediately if a command exits with a non-zero status. I'm using this often in scripts.
#!/bin/sh
set -e
# here goes the rest
-e, but you use -x in your example. Also, you could just put it in your shebang: #!/bin/sh -e.