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bash:globs [2019/12/07 13:04] – peterbash:globs [2021/02/04 09:43] (current) – [Glob Star - globstar] peter
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 ====== BASH - Globs ====== ====== BASH - Globs ======
  
-"Glob" is the common name for a set of Bash features that match or expand specific types of patterns.+**Glob** or **Globstar** is the common name for a set of Bash features that match or expand specific types of patterns.
  
 Some synonyms for globbing (depending on the context in which it appears) are pattern matching, pattern expansion, filename expansion, and so on. Some synonyms for globbing (depending on the context in which it appears) are pattern matching, pattern expansion, filename expansion, and so on.
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 A glob may look like ***.txt** and, when used to match filenames, is sometimes called a "wildcard". A glob may look like ***.txt** and, when used to match filenames, is sometimes called a "wildcard".
  
-Traditional shell globs use a very simple syntax, which is less expressive than a RegularExpression.+Traditional shell globs use a very simple syntax, which is less expressive than a Regular Expression.
  
 Most characters in a glob are treated literally, but a * matches 0 or more characters, a ? matches precisely one character, and [...] matches any single character in a specified set (see Ranges below). Most characters in a glob are treated literally, but a * matches 0 or more characters, a ? matches precisely one character, and [...] matches any single character in a specified set (see Ranges below).
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 tar xvf *.tar tar xvf *.tar
 # Expands to: tar xvf file1.tar file2.tar file42.tar ... # Expands to: tar xvf file1.tar file2.tar file42.tar ...
-# (which is generally not what one wants) 
 </code> </code>
  
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 # This is safe even if a filename contains whitespace: # This is safe even if a filename contains whitespace:
 for f in *.tar; do for f in *.tar; do
-    tar tvf "$f"+  tar tvf "$f"
 done done
  
 # But this one is not: # But this one is not:
 for f in $(ls | grep '\.tar$'); do for f in $(ls | grep '\.tar$'); do
-    tar tvf "$f"+  tar tvf "$f"
 done done
 </code> </code>
  
-In the second example above, the output of **ls** is filtered, and then the result of the whole pipeline is divided into words, to serve as iterative values for the loop.+<WRAP info> 
 +**NOTE:**  In the second example above, the output of **ls** is filtered, and then the result of the whole pipeline is divided into words, to serve as iterative values for the loop.
  
 This word-splitting will occur at internal whitespace within each filename, which makes it useless in the general case. This word-splitting will occur at internal whitespace within each filename, which makes it useless in the general case.
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 For more such examples, see BashPitfalls. For more such examples, see BashPitfalls.
 +
 +</WRAP>
  
 ---- ----
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 <code bash> <code bash>
 case "$input" in case "$input" in
-    [Yy]|'') confirm=1;; +  [Yy]|'') confirm=1;; 
-    [Nn]*) confirm=0;; +  [Nn]*) confirm=0;; 
-    *) echo "I don't understand.  Please try again.";;+  *) echo "I don't understand.  Please try again.";;
 esac esac
 </code> </code>
  
-Patterns (which are separated by | characters) are matched against the first word after the case itself.+<WRAP info> 
 +**NOTE:**  Patterns (which are separated by | characters) are matched against the first word after the case itself.
  
 The first pattern which matches, "wins", causing the corresponding commands to be executed. The first pattern which matches, "wins", causing the corresponding commands to be executed.
 +
 +</WRAP>
  
 ---- ----
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 |<nowiki>[[:digit:]_.]</nowiki>|Matches any digit, or _ or .| |<nowiki>[[:digit:]_.]</nowiki>|Matches any digit, or _ or .|
  
-In most shell implementations, one may also use ^ as the range negation character, e.g. [^[:space:]].+<WRAP info> 
 +**NOTE:**  In most shell implementations, one may also use ^ as the range negation character, e.g. [^[:space:]].
  
 However, POSIX specifies ! for this role, and therefore ! is the standard choice. However, POSIX specifies ! for this role, and therefore ! is the standard choice.
  
 Recent Bash versions Interpret [a-d] as [abcd].  To match a literal **-**, include it as first or last character. Recent Bash versions Interpret [a-d] as [abcd].  To match a literal **-**, include it as first or last character.
 +
 +</WRAP>
  
 ---- ----
  
-===== Options which change globbing behaviour =====+===== Options which change globbing behavior =====
  
 ==== Extended Globs - extglob ==== ==== Extended Globs - extglob ====
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 </code> </code>
  
-Patterns in a list are separated by | characters.+<WRAP info> 
 +**NOTE:**  Patterns in a list are separated by | characters. 
 +</WRAP> 
  
 ---- ----
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 # To remove all the files except ones matching *.jpg: # To remove all the files except ones matching *.jpg:
 rm !(*.jpg) rm !(*.jpg)
 +
 # All except *.jpg and *.gif and *.png: # All except *.jpg and *.gif and *.png:
 rm !(*.jpg|*.gif|*.png) rm !(*.jpg|*.gif|*.png)
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 <code bash> <code bash>
-# To copy all the MP3 songs except one to your device+# To copy all the MP3 songs except one to your device.
 cp !(04*).mp3 /mnt cp !(04*).mp3 /mnt
 </code> </code>
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 <code bash> <code bash>
-# To trim leading and trailing whitespace from a variable+# To trim leading and trailing whitespace from a variable.
 x=${x##+([[:space:]])}; x=${x%%+([[:space:]])} x=${x##+([[:space:]])}; x=${x%%+([[:space:]])}
 </code> </code>
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 </code> </code>
  
-extglob changes the way certain characters are parsed.+
  
 <WRAP info> <WRAP info>
-It is necessary to have a newline (not just a semicolon) between shopt -s extglob and any subsequent commands to use it.+**NOTE:**  extglob changes the way certain characters are parsed. 
 + 
 +It is necessary to have a newline (not just a semicolon) between **shopt -s extglob** and any subsequent commands to use it.
  
 You cannot enable extended globs inside a group command that uses them, because the entire block is parsed before the **shopt** is evaluated. You cannot enable extended globs inside a group command that uses them, because the entire block is parsed before the **shopt** is evaluated.
  
-Note that the typical function body is a group command. An unpleasant workaround could be to use a subshell command list as the function body.+The typical function body is a group command.  An unpleasant workaround could be to use a subshell command list as the function body.
 </WRAP> </WRAP>
  
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 <code bash> <code bash>
 #!/usr/bin/env bash #!/usr/bin/env bash
-shopt -s extglob   # and others, such as nullglob dotglob+shopt -s extglob   # and others, such as nullglob dotglob.
 </code> </code>
  
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 <code bash> <code bash>
-# remember whether extglob was originally set, so we know whether to unset it+# Remember whether extglob was originally set, so we know whether to unset it.
 shopt -q extglob; extglob_set=$? shopt -q extglob; extglob_set=$?
-# set extglob if it wasn't originally set.+# Set extglob if it wasn't originally set.
 ((extglob_set)) && shopt -s extglob ((extglob_set)) && shopt -s extglob
 # Note, 0 (true) from shopt -q is "false" in a math context. # Note, 0 (true) from shopt -q is "false" in a math context.
  
 # The basic concept behind the following is to delay parsing of the globs until evaluation. # The basic concept behind the following is to delay parsing of the globs until evaluation.
-# This matters at group commands, such as functions in { } blocks+# This matters at group commands, such as functions in { } blocks.
  
 declare -a s='( !(x) )' declare -a s='( !(x) )'
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 eval 'echo !(x)'  # using eval if no other option. eval 'echo !(x)'  # using eval if no other option.
  
-# unset extglob if it wasn't originally set+# Unset extglob if it wasn't originally set.
 ((extglob_set)) && shopt -u extglob ((extglob_set)) && shopt -u extglob
  
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 ls: cannot access *.c: No such file or directory ls: cannot access *.c: No such file or directory
  
-# with nullglob set+# With nullglob set.
 shopt -s nullglob shopt -s nullglob
 ls *.c ls *.c
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 <WRAP important> <WRAP important>
-**Warning:**  Enabling nullglob on a wide scope can trigger bugs caused by bad programming practices.+**WARNING:**  Enabling nullglob on a wide scope can trigger bugs caused by bad programming practices.
  
 It "breaks" the expectations of many utilities. It "breaks" the expectations of many utilities.
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 shopt -s nullglob shopt -s nullglob
 array=([1]=*) array=([1]=*)
-#results in an empty array+# Results in an empty array.
 </code> </code>
  
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 for x in *; do for x in *; do
-    [ -e "$x" ] || break +  [ -e "$x" ] || break 
-    ...+  ...
 done done
  
 f() { f() {
-    [ -e "$1" ] || return 1+  [ -e "$1" ] || return 1
  
-    for x do +  for x do 
-        ... +    ... 
-    done+  done
 } }
  
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 for x in ~(N)*; do for x in ~(N)*; do
-    ...+  ...
 done done
 </code> </code>
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 (since bash 4.0-alpha) (since bash 4.0-alpha)
  
-globstar recursively repeats a pattern containing '**'.+globstar recursively repeats a pattern containing **<nowiki>**</nowiki>**.
  
 <code bash> <code bash>
-$ shopt -s globstar; tree+shopt -s globstar; tree
 . .
 ├── directory2 ├── directory2
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 </code> </code>
  
-# Suppose that for the following examples.+Suppose that for the following examples.
  
 Matching files: Matching files:
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 </code> </code>
  
-Just like '*', '**' followed by a '/' will only match directories:+<WRAP info> 
 +**NOTE:**  To disable globstar use 
 + 
 +<code bash> 
 +shopt -u globstar 
 +</code> 
 + 
 +See:  **help shopt** for details. 
 +</WRAP> 
 + 
 + 
 +---- 
 + 
 +Assume you have a folder structure: 
 + 
 +<code> 
 +. 
 +├── bar 
 +│   ├── foo 
 +│   │   └── baz 
 +│   │       └── hurz 
 +│   │           └── lolz 
 +│   │               └── hello.txt 
 +│   └── poit.txt 
 +└── fnord.txt 
 +</code> 
 + 
 +Then **ls** with single star **<nowiki>*</nowiki>** would list: 
 + 
 +<code bash> 
 +ls *.txt 
 +fnord.txt 
 +</code> 
 + 
 +The double star operator **<nowiki>**</nowiki>** will work on the subfolders.  The output will look like: 
 + 
 +<code bash> 
 +ls **/*.txt 
 +bar/foo/baz/hurz/lolz/hello.txt  bar/poit.txt  fnord.txt 
 +</code> 
 + 
 +---- 
 + 
 +<WRAP info> 
 +**NOTE:**  Just like **<nowiki>*</nowiki>**, **<nowiki>**</nowiki>** followed by a **<nowiki>/</nowiki>** will only match directories: 
 +</WRAP> 
  
 <code bash> <code bash>
-$ files=(**/) +files=(**/) 
-# finds all subdirectories+# Finds all subdirectories.
  
-$ files=(. **/) +files=(. **/) 
-# finds all subdirectories, including the current directory +# Finds all subdirectories, including the current directory. 
-# corresponds to: find -type d+# Corresponds to: find -type d.
 </code> </code>
  
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 <code bash> <code bash>
 foo() { foo() {
-   local f r=0 nc=0 +  local f r=0 nc=0 
-   shopt -q nocasematch && nc=1 || shopt -s nocasematch +  shopt -q nocasematch && nc=1 || shopt -s nocasematch 
-   for f; do +  for f; do 
-      [[ $f = *.@(txt|jpg) ]] || continue +    [[ $f = *.@(txt|jpg) ]] || continue 
-      cmd -on "$f" || r=1 +    cmd -on "$f" || r=1 
-   done +  done 
-   ((nc)) || shopt -u nocasematch +  ((nc)) || shopt -u nocasematch 
-   return $r+  return $r
 } }
 </code> </code>
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 <code bash> <code bash>
 case $f in case $f in
-    *.[Tt][Xx][Tt]|*.[Jj][Pp][Gg]) : ;; +  *.[Tt][Xx][Tt]|*.[Jj][Pp][Gg]) : ;; 
-    *) continue+  *) continue
 esac esac
 </code> </code>
bash/globs.1575723863.txt.gz · Last modified: 2020/07/15 09:30 (external edit)
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