shellコマンドを読み解くコツ

shellコマンドを読み解く際のTipsをメモします。

はじめに
shellコマンドを読み解く
おわりに
参考

はじめに

こんにちは、@bioerrorlogです。

自分の知らない複雑なコマンドに出会ったときにさっと読み解けると、生産性が上がります。昔は私も無駄にググって時間を浪費してました。

今回は過去の自分に教えるつもりで、コマンドを読み解くときのコツ/流れをメモしておきます。

shellコマンドを読み解く

--helpオプションを使う

とりあえずざっとコマンドの内容を把握するには--helpオプションを使うのがお手軽です。

大体どのコマンドにも--helpオプションは用意されているので、初見のコマンドやよくわからないコマンドに遭遇した時はさっと--helpを見るのがおすすめです。 (仮に--helpが用意されていなくても、だいたいはそのままUSAGE/使用方法が表示されるので問題ありません)

例

$ git --help
usage: git [--version] [--help] [-C <path>] [-c <name>=<value>]
           [--exec-path[=<path>]] [--html-path] [--man-path] [--info-path]
           [-p | --paginate | -P | --no-pager] [--no-replace-objects] [--bare]
           [--git-dir=<path>] [--work-tree=<path>] [--namespace=<name>]
           <command> [<args>]

These are common Git commands used in various situations:

start a working area (see also: git help tutorial)
   clone             Clone a repository into a new directory
   init              Create an empty Git repository or reinitialize an existing one

work on the current change (see also: git help everyday)
   add               Add file contents to the index
   mv                Move or rename a file, a directory, or a symlink
   restore           Restore working tree files
   rm                Remove files from the working tree and from the index
   sparse-checkout   Initialize and modify the sparse-checkout

examine the history and state (see also: git help revisions)
   bisect            Use binary search to find the commit that introduced a bug
   diff              Show changes between commits, commit and working tree, etc
   grep              Print lines matching a pattern
   log               Show commit logs
   show              Show various types of objects
   status            Show the working tree status

grow, mark and tweak your common history
   branch            List, create, or delete branches
   commit            Record changes to the repository
   merge             Join two or more development histories together
   rebase            Reapply commits on top of another base tip
   reset             Reset current HEAD to the specified state
   switch            Switch branches
   tag               Create, list, delete or verify a tag object signed with GPG

collaborate (see also: git help workflows)
   fetch             Download objects and refs from another repository
   pull              Fetch from and integrate with another repository or a local branch
   push              Update remote refs along with associated objects

'git help -a' and 'git help -g' list available subcommands and some
concept guides. See 'git help <command>' or 'git help <concept>'
to read about a specific subcommand or concept.
See 'git help git' for an overview of the system.

manコマンドを使う

もう少し詳しい説明が欲しい時は、manコマンドでマニュアルページを表示するのも手です。 --helpの記述よりも詳細な説明を読むことができます。

例: man git

GIT(1)                                                                                        Git Manual                                                                                       GIT(1)

NAME
       git - the stupid content tracker

SYNOPSIS
       git [--version] [--help] [-C <path>] [-c <name>=<value>]
           [--exec-path[=<path>]] [--html-path] [--man-path] [--info-path]
           [-p|--paginate|-P|--no-pager] [--no-replace-objects] [--bare]
           [--git-dir=<path>] [--work-tree=<path>] [--namespace=<name>]
           [--super-prefix=<path>]
           <command> [<args>]

DESCRIPTION
       Git is a fast, scalable, distributed revision control system with an unusually rich command set that provides both high-level operations and full access to internals.

       See gittutorial(7) to get started, then see giteveryday(7) for a useful minimum set of commands. The Git User’s Manual[1] has a more in-depth introduction.

       After you mastered the basic concepts, you can come back to this page to learn what commands Git offers. You can learn more about individual Git commands with "git help command". gitcli(7)
       manual page gives you an overview of the command-line command syntax.

       A formatted and hyperlinked copy of the latest Git documentation can be viewed at https://git.github.io/htmldocs/git.html or https://git-scm.com/docs.

OPTIONS
       --version
           Prints the Git suite version that the git program came from.

       --help
           Prints the synopsis and a list of the most commonly used commands. If the option --all or -a is given then all available commands are printed. If a Git command is named this option will
           bring up the manual page for that command.

           Other options are available to control how the manual page is displayed. See git-help(1) for more information, because git --help ...  is converted internally into git help ....

       -C <path>
           Run as if git was started in <path> instead of the current working directory. When multiple -C options are given, each subsequent non-absolute -C <path> is interpreted relative to the
           preceding -C <path>. If <path> is present but empty, e.g.  -C "", then the current working directory is left unchanged.

           This option affects options that expect path name like --git-dir and --work-tree in that their interpretations of the path names would be made relative to the working directory caused by
           the -C option. For example the following invocations are equivalent:

               git --git-dir=a.git --work-tree=b -C c status
               git --git-dir=c/a.git --work-tree=c/b status

       -c <name>=<value>
           Pass a configuration parameter to the command. The value given will override values from configuration files. The <name> is expected in the same format as listed by git config (subkeys
           separated by dots).

           Note that omitting the = in git -c foo.bar ...  is allowed and sets foo.bar to the boolean true value (just like [foo]bar would in a config file). Including the equals but with an empty
           value (like git -c foo.bar= ...) sets foo.bar to the empty string which git config --type=bool will convert to false.

       --exec-path[=<path>]
           Path to wherever your core Git programs are installed. This can also be controlled by setting the GIT_EXEC_PATH environment variable. If no path is given, git will print the current
           setting and then exit.

 Manual page git(1) line 1 (press h for help or q to quit)