Diff for "BashFAQ/041"

Differences between revisions 1 and 14 (spanning 13 versions)

How do I determine whether a variable contains a substring?

in BASH, to match using pattern matching:

  # Bash
  if [[ $foo == *bar* ]]

Portable POSIX sh syntax:

  # Bourne
  case $foo in
    *bar*) .... ;;
  esac

The case allows matching variables against globbing-style patterns. In Bash, and some shells, there is also extended globs.

In Bash, to match using regular expressions:

  # Bash 3.x
  # matches e.g ac, abc and abbbbc
  re='ab*c'
  if [[ $foo =~ $re ]]

Portable POSIX sh syntax to match using regular expressions:

  # POSIX
  if expr "x$foo" : 'x.*bar' > /dev/null
  then 
      ...
  fi

For more hints on string manipulations in Bash, see FAQ #100.

CategoryShell

-  ⇤ ← Revision 1 as of 2007-05-02 23:31:14 → 
  Size: 730
  Editor: redondos
  Comment:
+   ← Revision 14 as of 2025-04-10 21:28:26 → ⇥
  Size: 853
  Editor: 81
  Comment: Simplify. Rm text "expr utility", already shown in code
-Deletions are marked like this.
+Additions are marked like this.
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-[[Anchor(faq41)]]
+<<Anchor(faq41)>>
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+in [[BASH]], to match using pattern matching:
-Line 5:
+Line 6:
-  if [[ $foo = *bar* ]]
+  # Bash
  if [[ $foo == *bar* ]]
-Line 8:
+Line 10:
-The above works in virtually all versions of Bash.  Bash version 3 also allows regular expressions:
+Portable POSIX sh syntax:
-Line 11:
+Line 13:
-  if [[ $foo =~ ab*c ]]   # bash 3, matches abbbbcde, or ac, etc.
}}}

If you are programming in the BourneShell instead of Bash, there is a more portable (but less pretty) syntax:

{{{
  case "$foo" in
+  # Bourne
  case $foo in
-Line 22:
+Line 19:
-This should allow you to match variables against globbing-style patterns.  if you need a portable way to match variables against regular expressions, use {{{grep}}} or {{{egrep}}}.
+The {{{case}}} allows matching variables against [[glob|globbing]]-style patterns. In Bash, and some shells, there is also extended globs.

In Bash, to match using regular expressions:
-Line 25:
+Line 24:
-  if echo "$foo" | egrep some-regex >/dev/null; then ...
+  # Bash 3.x
  # matches e.g ac, abc and abbbbc
  re='ab*c'
  if [[ $foo =~ $re ]]
-Line 27:
+Line 29:
+Portable POSIX sh syntax to match using [[RegularExpression|regular expressions]]:

{{{
  # POSIX
  if expr "x$foo" : 'x.*bar' > /dev/null
  then 
      ...
  fi
}}}

For more hints on string manipulations in Bash, see [[BashFAQ/100|FAQ #100]].


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CategoryShell