Diff for "BashFAQ/067"

Differences between revisions 9 and 12 (spanning 3 versions)

How can I trim leading/trailing white space from one of my variables?

There are a few ways to do this:

   #POSIX, but fails if the variable contains newlines
   read -r var << EOF
   $var
   EOF

The easiest and cleanest way is with a bash herestring:

   read  -rd '' x <<< "$x"

Using an empty string as a delimiter means the read consumes the whole string, as NUL is used. (Remember: BASH only does C-string variables.) This is entirely safe for any text, including newlines.

There's also a solution using extglob which shows how you can use it in parameter expansion:

   # Bash
   shopt -s extglob
   x=${x##+([[:space:]])} x=${x%%+([[:space:]])}
   shopt -u extglob

This also works in KornShell, without needing the explicit extglob setting:

   # ksh
   x=${x##+([[:space:]])} x=${x%%+([[:space:]])}

There are many, many other ways to do this, using sed for instance:

   # POSIX, suppress the trailing and leading whitespace on every lines
   x=$(echo "$x" | sed -e 's/^[[:space:]]*//' -e 's/[[:space:]]*$//')

-  ⇤ ← Revision 9 as of 2008-07-17 15:56:11 → 
  Size: 1107
  Editor: wsip-68-15-32-50
  Comment:
+   ← Revision 12 as of 2009-05-10 03:42:31 → ⇥
  Size: 1130
  Editor: localhost
  Comment: igli: *sigh* BASH handles strings fine. m00 gc ;-)
-Deletions are marked like this.
+Additions are marked like this.
 Line 3:
 There are a few ways to do this:
 Line 8:
-   $var 
   EOF
+   $var
   EOF
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-One can also achieve in bash using a herestring
+The easiest and cleanest way is with a bash herestring:
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-   # Bash still fails if the variable contains a newline.
   read  -r x <<< "$x"
+   read  -rd '' x <<< "$x"
-Line 17:
+Line 16:
+Using an empty string as a delimiter means the read consumes the whole string, as NUL is used. (Remember: BASH only does C-string variables.) This is entirely safe for any text, including newlines.
 Line 18:
-(note: using IFS=$' \t' read -d "" -r x partially fix the "problem" of the newlines but adds a trailing \n)

There's also a solution using [:glob:extglob]:
+There's also a solution using [[glob|extglob]] which shows how you can use it in parameter expansion:
-Line 36:
+Line 33:
 There are many, many other ways to do this, using sed for instance:
-Line 41:
+Line 38:
-These are not necessarily the best, but they're known to work.