Diff for "BashFAQ/067"

Differences between revisions 6 and 12 (spanning 6 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 6 as of 2008-07-04 09:01:07 → 
  Size: 883
  Editor: pgas
  Comment: posix solution with a here string
+   ← 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.
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-[[Anchor(faq67)]]
+<<Anchor(faq67)>>
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-There are a few ways to do this
+There are a few ways to do this:
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-   #POSIX
+   #POSIX, but fails if the variable contains newlines
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-   $var 
   EOF
+   $var
   EOF
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+Line 12:
-One can also achieve in bash (and ksh93) using a herestring
+The easiest and cleanest way is with a bash herestring:
{{{
   read  -rd '' x <<< "$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.
-Line 13:
+Line 18:
-{{{
   # Bash
   # Remove leading whitespace:
   read -r x <<< "$x"
}}}

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 35:
+Line 33:
 There are many, many other ways to do this, using sed for instance:
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+Line 35:
-   # POSIX
+   # POSIX, suppress the trailing and leading whitespace on every lines
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+Line 38:
-These are not necessarily the best, but they're known to work.