Lady’s Gitweb - HOMEDIR/blob - sh/githooks/pre-commit.sh

   1 #!/usr/bin/env sh
   2 # @(#)🏠📂 HOMEDIR sh/githooks/pre-commit.sh       2026-03-22T02:03:39Z
   3 # SPDX-FileCopyrightText: 2026 Lady <https://www.ladys.computer/about/#lady>
   4 # SPDX-License-Identifier: MPL-2.0
   5
   6 ## ⁌ Git Pre‐Commit
   7 ##
   8 ## ∎ Copyright © 2026 Lady [@ Ladys Computer].
   9 ##
  10 ## ⋮ This Source Code Form is subject to the terms of the Mozilla
  11 ##   Public License, version 2.0.
  12 ## If a copy of the M·P·L was not distributed with this file, You can
  13 ##   obtain one at {🔗<https://mozilla.org/MPL/2.0/>}.
  14
  15 ## § Description
  16 ##
  17 ## This script performs actions on files prior to a Git commit being
  18 ##   made.
  19 ## It is intended to be used as a precommit hook in a Git repository.
  20 ##
  21 ## ❦ “What” signature updates
  22 ##
  23 ## This script checks the first 24 lines of each file that is currently
  24 ##   staged in the index (i·e which will be committed) for the string
  25 ##   `@({U+23})´.
  26 ## It takes this, and all following characters up to the next newline
  27 ##   or tab (which are assumed to be a product name), and deletes
  28 ##   everything which follows on that line.
  29 ## Then it appends to the line the following items, each preceded by a
  30 ##   tab :⁠—
  31 ##
  32 ## • The path to the file, relative to the repository root.
  33 ##
  34 ## • The current date and time.
  35 ##
  36 ## This operation is applied both on the version of the file staged in
  37 ##   the index and on the one in the working tree.
  38 ##
  39 ## The result of this change is that calling What (a Posix development
  40 ##   utility) on the file will provide the associated project name,
  41 ##   path, and datetime (of last commit) for the file.
  42 ## This is useful in situations where more sophisticated versioning
  43 ##   identification (e·g `git describe´) is not available.
  44 ##
  45 ## If a file does not contain the sequence `@({U+23})´ in its first 24
  46 ##   lines, no changes are made.
  47
  48 ## § Configuration
  49 ##
  50 ## The following variables provide hooks to override the commands used
  51 ##   by this script.
  52
  53 : "${cmd_DATE:=date}"
  54 : "${cmd_GIT:=git}"
  55 : "${cmd_GREP:=grep}"
  56 : "${cmd_HEAD:=head}"
  57 : "${cmd_PRINTF:=printf}"
  58 : "${cmd_SED:=sed}"
  59 : "${cmd_TEST:=test}"
  60 : "${cmd_TR:=tr}"
  61 : "${cmd_WC:=wc}"
  62 : "${cmd_XARGS:=xargs}"
  63
  64 ## § Implementation
  65 ##
  66 ## `IFS´ is made null to prevent line splitting and `LC_ALL´ is set to
  67 ##   the Posix (C) locale.
  68
  69 IFS=
  70 LC_ALL=C
  71
  72 ## The `now´ variable simply holds the current datetime.
  73
  74 now="$(
  75   TZ=UTC0 "${cmd_DATE}" -u '+%Y-%m-%dT%H:%M:%SZ'
  76 )"
  77
  78 ## The `modified´ variable provides a list of changed text files.
  79 ## The `--diff-filter´ excludes deleted files and the `--eol´ check is
  80 ##   used to exclude binary files.
  81
  82 modified="$(
  83   "${cmd_GIT}" diff -z \
  84     --cached --name-only --no-renames \
  85     --diff-filter=d |
  86   "${cmd_XARGS}" -0 "${cmd_GIT}" ls-files --eol -- |
  87   "${cmd_SED}" '/^i[/]-text/d;s/^.*     //'
  88 )"
  89
  90 ## If no files were modified, do nothing.
  91
  92 if "${cmd_TEST}" -z "${modified}"
  93 then :
  94   exit
  95 fi
  96
  97 ## The `makepatch´ function provides the main implementation.
  98 ## It takes a blob of text (`blob´) and prints a diff that Git can
  99 ##   apply which makes the necessary changes.
 100 ## If no changes are necessary, it returns an empty string.
 101
 102 makepatch () {
 103
 104 ## The `whatline´ variable holds the line number of the `@({U+23})´
 105 ##   string within the blob.
 106 ## This function prints nothing unless `whatline´ holds a value.
 107
 108   whatline="$(
 109     "${cmd_PRINTF}" '%s\n' "${blob}" |
 110     "${cmd_GREP}" -n '@([#])' |
 111     "${cmd_HEAD}" -n 1 |
 112     "${cmd_SED}" 's/^\([^:]*\):.*$/\1/'
 113   )"
 114
 115 ## Up to five lines following the line indicated by `whatline´ are
 116 ##   included as context in the resulting diff.
 117
 118   if "${cmd_TEST}" -n "${whatline}"
 119   then :
 120     context="$(
 121       "${cmd_PRINTF}" '%s\n' "${blob}" |
 122       "${cmd_HEAD}" -n $((${whatline} + 5))
 123     )"
 124     diff="$(
 125
 126 ## First, the diff includes lines up to `whatline´ with no
 127 ##   modifications, and deletes the `whatline´ line as it currently
 128 ##   exists.
 129
 130       "${cmd_PRINTF}" '%s\n' "${context}" |
 131       "${cmd_SED}" \
 132         -e $((${whatline} + 1))',$d' \
 133         -e "${whatline}"'!s/^/ /' \
 134         -e "${whatline}"'s/^/-/'
 135
 136 ## An updated version of the `whatline´ line is then inserted.
 137
 138       {
 139         "${cmd_PRINTF}" '%s\n' "${context}" |
 140         "${cmd_SED}" \
 141           -e "${whatline}"'!d' \
 142           -e "${whatline}"'s/\(@([#])[^ ]*\)\(  .*\)*/\1/' \
 143           -e 's/^/+/' |
 144         "${cmd_TR}" -d '\n'
 145         "${cmd_PRINTF}" '\t%s' "${file}" "${now}"
 146         "${cmd_PRINTF}" '%s\n' ''
 147       } |
 148       "${cmd_SED}" 's/  *$//'
 149
 150 ## Finally, lines whose indices follow `whatline´ are included with·out
 151 ##   modifications.
 152
 153       "${cmd_PRINTF}" '%s\n' "${context}" |
 154       "${cmd_SED}" \
 155         -e '1,'"${whatline}"'d' \
 156         -e 's/^/ /'
 157     )"
 158
 159 ## The number of lines in  the resulting diff cannot be assumed and
 160 ##   must be counted.
 161 ## The diff always starts at index 1 and has a context length 1 less
 162 ##   than its number of lines (because the deletion and addition affect
 163 ##   the same line of content).
 164
 165     difflen="$(
 166       "${cmd_PRINTF}" '%s\n' "${diff}" |
 167       "${cmd_WC}" -l
 168     )"
 169     diffend=$((${difflen} - 1))
 170
 171 ## The diff is printed in a rough `diff --git´ format.
 172
 173     "${cmd_PRINTF}" '%s\n' \
 174       'diff --git "a/'"${file}"'" "b/'"${file}"'"' \
 175       '--- "a/'"${file}"'"' \
 176       '+++ "b/'"${file}"'"' \
 177       '@@ -1,'"${diffend}"' +1,'"${diffend}"' @@' \
 178       "${diff}"
 179   fi
 180 }
 181
 182 ## Staged files are read and the diffs are applied to them when
 183 ##   applicable.
 184 ## Files in the working directory are only updated after changes to the
 185 ##   index succeed.
 186
 187 "${cmd_PRINTF}" '%s\n' "${modified}" |
 188 while read -r file
 189 do :
 190   indexblob="$(
 191     "${cmd_GIT}" cat-file blob ':'"${file}" |
 192     "${cmd_HEAD}" -n 24
 193   )"
 194   indexpatch="$(
 195     blob="${indexblob}" makepatch
 196   )"
 197   if "${cmd_TEST}" -n "${indexpatch}"
 198   then :
 199     "${cmd_PRINTF}" '%s\n' "${indexpatch}" |
 200     "${cmd_GIT}" apply --cached
 201     workingblob="$(
 202       "${cmd_HEAD}" -n 24 -- "${file}"
 203     )"
 204     workingpatch="$(
 205       blob="${workingblob}" makepatch
 206     )"
 207     if "${cmd_TEST}" -n "${workingpatch}"
 208     then :
 209       "${cmd_PRINTF}" '%s\n' "${workingpatch}" |
 210       "${cmd_GIT}" apply
 211     fi
 212   fi
 213 done