Scripts in linux start with some declaration like :
#!/bin/bash
Correct me if I am wrong : this probably says which shell to use.
I have also seen some scripts which say :
#!/bin/bash -ex
what is the use of the flags -ex
3 Answers
#!/bin/bash -ex
<=>
#!/bin/bash
set -e -x
Man Page (http://ss64.com/bash/set.html):
-e Exit immediately if a simple command exits with a non-zero status, unless
the command that fails is part of an until or while loop, part of an
if statement, part of a && or || list, or if the command's return status
is being inverted using !. -o errexit
-x Print a trace of simple commands and their arguments
after they are expanded and before they are executed. -o xtrace
UPDATE:
BTW, It is possible to set switches without script modification.
For example we have the script t.sh:
#!/bin/bash
echo "before false"
false
echo "after false"
And would like to trace this script: bash -x t.sh
output:
+ echo 'before false'
before false
+ false
+ echo 'after false'
after false
For example we would like to trace script and stop if some command fail (in our case it will be done by command false): bash -ex t.sh
output:
+ echo 'before false'
before false
+ false
Comments
These are documented under set in the SHELL BUILTIN COMMANDS section of the man page:
-ewill cause Bash to exit as soon as a pipeline (or simple line) returns an error-xwill case Bash to print the commands before executing them
Comments
-e
is to quit the script on any error
-x
is the debug mode
Check bash -x command and What does set -e mean in a bash script?
help setfor more details on these flags...