commands:builtin:mapfile

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commands:builtin:mapfile [2011/11/18 05:51]
ormaaj Simplify and bugfix I didn't notice because I use lastpipe.
commands:builtin:mapfile [2013/04/14 12:37]
thebonsai Don't tread version 4 special - it has been around for a long time now
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 ====== The mapfile builtin command ====== ====== The mapfile builtin command ======
-:V4: 
  
 ===== Synopsis ===== ===== Synopsis =====
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 </​code>​ </​code>​
  
-===== Bugs =====+This example based on yet another #bash question illustrates mapfile in combination with read. The sample input is the heredoc to ''​main''​. The goal is to build a "​struct"​ based upon records in the input file made up of the numbers following the colon on each line. Every 3rd line is a key followed by 2 corresponding fields. The showRecord function takes a key and returns the record.
  
-  ​Early implementations were buggy. For example, ''​mapfile'' ​filling the readline history buffer with calls to the ''​CALLBACK''​. ​This was fixed in 4.1 betaSome bugs may still exist.+<​code>​ 
 +#​!/​usr/​bin/​env bash 
 + 
 +showRecord() { 
 +    printf '​key[%d] = %d, %d\n' "​$1"​ "​${vals[@]:​keys[$1]*2:​2}"​ 
 +
 + 
 +parseRecords() { 
 +    trap 'unset -f _f' RETURN 
 +    _f() { 
 +        local x 
 +        IFS=: read -r _ x 
 +        ((keys[x]=n++)) 
 +    } 
 +    local n 
 + 
 +    _f 
 +    mapfile -tc2 -C _f "​$1"​ 
 +    eval "​$1"'​=("​${'"​$1"'​[@]##​*:​}"​)'​ # Return the array with some modification 
 +
 + 
 +main() { 
 +    local -a keys vals 
 +    parseRecords vals 
 +    showRecord "​$1"​ 
 +
 + 
 +main "​$1"​ <<​-"​EOF"​ 
 +fabric.domain:​123 
 +routex:1 
 +routey:2 
 +fabric.domain:​321 
 +routex:6 
 +routey:4 
 +EOF 
 +</​code>​ 
 + 
 +For example, ​running ''​scriptname 321''​ would output ''​key[321] = 6, 4''​. Every 2 lines read by ''​mapfile''​the function ​''​_f'' ​is called, which reads one additional lineSince the first line in the file is a key, and ''​_f''​ is responsible for the keys, it gets called first so that ''​mapfile''​ starts by reading the second line of input, calling ''​_f''​ with each subsequent 2 iterationsThe RETURN trap is unimportant. 
 +===== Bugs =====
  
 +  * Early implementations were buggy. For example, ''​mapfile''​ filling the readline history buffer with calls to the ''​CALLBACK''​. This was fixed in 4.1 beta.
 +  * <​del>''​mapfile -n''​ reads an extra line beyond the last line assigned to the array, through Bash.</​del>​ [[ftp://​ftp.gnu.org/​gnu/​bash/​bash-4.2-patches/​bash42-035 | Fixed in 4.2.35]].
 ===== To Do ===== ===== To Do =====
   * Create an implementation as a shell function that's portable between Ksh, Zsh, and Bash (and possibly other bourne-like shells with array support).   * Create an implementation as a shell function that's portable between Ksh, Zsh, and Bash (and possibly other bourne-like shells with array support).
  • commands/builtin/mapfile.txt
  • Last modified: 2013/08/19 08:09
  • by ormaaj