Diff for "BashFAQ/041"

Differences between revisions 4 and 16 (spanning 12 versions)

How do I determine whether a variable contains a substring?

in BASH, to match using pattern matching:

  if [[ $foo == *bar* ]]; then
    ...
  fi

Portable POSIX sh syntax:

  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 3.x or later, to match using regular expressions:

  # matches e.g ac, abc and abbbbc
  re='ab*c'
  if [[ $foo =~ $re ]]; then
    ...
  fi

Portable POSIX sh syntax to match using regular expressions. Notice that the initial ".*" is required:

  if expr "$foo" : ".*$re" > /dev/null
  then 
      ...
  fi

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

CategoryShell

-  ⇤ ← Revision 4 as of 2008-05-16 20:00:06 → 
  Size: 747
  Editor: GreyCat
  Comment: add link
+   ← Revision 16 as of 2025-04-10 22:22:40 → ⇥
  Size: 912
  Editor: 81
  Comment: Code: adjust if, simplify expr
-Deletions are marked like this.
+Additions are marked like this.
 Line 1:
-[[Anchor(faq41)]]
+<<Anchor(faq41)>>
 Line 3:
+in [[BASH]], to match using pattern matching:
-Line 5:
+Line 6:
-  if [[ $foo = *bar* ]]
+  if [[ $foo == *bar* ]]; then
    ...
  fi
-Line 8:
+Line 11:
-The above works in virtually all versions of Bash.  Bash version 3 also allows regular expressions:
+Portable POSIX sh syntax:
-Line 11:
+Line 14:
-  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
    *bar*) .... ;;
+  case $foo in
    *bar*) ...
           ;;
-Line 22:
+Line 20:
-{{{case}}} allows you to match variables against [:globbing:]-style patterns.  If you need a portable way to match variables against [:RegularExpression: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 3.x or later, to match using regular expressions:
 Line 25:
-  if echo "$foo" | grep bar >/dev/null; then ...
+  # matches e.g ac, abc and abbbbc
  re='ab*c'
  if [[ $foo =~ $re ]]; then
    ...
  fi
-Line 27:
+Line 31:
+Portable POSIX sh syntax to match using [[RegularExpression|regular expressions]]. Notice that the initial ".*" is required:

{{{
  if expr "$foo" : ".*$re" > /dev/null
  then 
      ...
  fi
}}}

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


----
CategoryShell