Editing Bash (Unix shell) (section)

==== Examples ====
With the {{code|:?|bash}} parameter expansion, an unset or null variable can halt a script.
* ex.sh
*: <syntaxhighlight lang="bash">
#!/bin/bash
bar="foo is not defined"
echo "${foo:?$bar}"
echo this message doesn't print
</syntaxhighlight>
*: <syntaxhighlight lang="console">
$ ./ex.sh
./ex.sh: line 3: foo: foo is not defined
</syntaxhighlight>

Reliably printing the contents of an array that contains spaces and newlines first in a portable syntax, and then the same thing in Bash. Note that in Bash, the number of spaces before the newline is made clear.
: <syntaxhighlight lang="console">
$ # In POSIX shell:
$ array=( "a" "b" "
>  c " )
$ printf ',%s,\n' "${array[@]}"
,a,
, b,
,
 c,
</syntaxhighlight>
: <syntaxhighlight lang="bash">
# In Bash:
declare -p array
declare -a array=([0]="a" [1]=" b" [2]=$' \n c ')
</syntaxhighlight>

Printing an error message when there's a problem.
* error.sh
*: <syntaxhighlight lang="bash">
if ! lsblk | grep sdb
then
  echo Error, line $LINENO
fi
</syntaxhighlight>
*: <syntaxhighlight lang="console">
$ ./error.sh
Error, line 130
</syntaxhighlight>

Using [[xtrace]]. If errexit had been enabled, then {{code|echo quux|bash}} would not have been executed.

* test.sh
*: <syntaxhighlight lang="bash">
#!/bin/bash
set -x
foo=bar; echo $foo
false
echo quux
</syntaxhighlight>
*: <syntaxhighlight lang="console">
$ ./test.sh
+ foo=bar
+ echo bar
bar
+ false
+ echo quux
quux
</syntaxhighlight>