The Art of Command Line (2021) https://www.slideshare.net/ykenta/the-art-of-command-line-2021

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The Art of Command Line

2021-02-22

Kenta Yamamoto (@i05)

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Unix Philosophy - "The Art of UNIX Programming" (2003)

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Make each program do one thing well. To do a new job, build afresh rather than complicate old programs by adding new features.

$ history | awk '{ print $2 }' | sort | uniq -c | awk '$1>1' | sort -r | head
    791 g
    172 cat
    115 git
     83 echo
     71 brew
     70 yarn
     68 ll
     50 dig
     49 gcloud
     43 jj

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For example, you have to sort the output before uniq because they only do one thing:

$ history | awk '{ print $2 }' | sort | uniq -c | awk '$1>1' | sort -r | head

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Execute a shell script:

#!/usr/bin/env bash
# command-ranking.sh
set -euo pipefail
history | awk '{ print $2 }' | sort | uniq -c | awk '$1>1' | sort -r

$ chmod u+x ./command-ranking.sh
$ bash ./command-ranking.sh | head

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Interface - standard streams:

• STDIN
• STDOUT
• STDERR

$ time curl -IL https://example.com/ 2>&1 > file.txt

$ time curl -IL https://example.com/
...
curl -IL https://example.com/  0.02s user 0.01s system 5% cpu 0.467 total

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Parameters - $0, $1, $#, $@

#!/usr/bin/env bash
# sample.sh
cat -
echo "file=$0, 1st-arg=$1, 2nd-arg=$2, arg-num=$# args=$@"

$ echo "Hello" | bash $(pwd)/sample.sh foo bar baz
Hello
file=/Users/kyamamoto/src/bitbucket.org/i05/support/sample.sh, 1st-arg=foo, 2nd-arg=bar, arg-num=3 args=foo bar baz

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Sounds of Silence - $?

$ touch ~/tmp/sample.txt
$ echo $?
0

$ mv no-such-file.txt /tmp/
mv: cannot stat 'no-such-file.txt': No such file or directory
$ echo $?
1

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Subroutine - $(command)

$ curl "https://jpnic.rdap.apnic.net/ip/$(dig +short myip.opendns.com @resolver1.opendns.com)" \
| jq .

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Construct argument list - xargs:

$ find . -type f -name "*" ! -path '*/.svn/*' ! -path '*/.git/*' -print0 \
| xargs -0 grep --ignore-case --line-number 'foo'

Parallel execution - xargs:

$ find . -type f -not -name '*.bz2' -print0 \
| xargs -0 -L 1 -P $(sysctl -n hw.ncpu) bzip2

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Multibyte encoding - nkf:

$ find . -type f -name "*.txt" | xargs nkf --guess
$ find . -type f -print0 | xargs -0 nkf --overwrite -w

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Multiline:

TEXT_LIST=$(cat << EOF
__HERE_DOCUMENT__
__HERE_DOCUMENT__
EOF
)

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Runs everywhere:

case "${OSTYPE}" in
# Mac
darwin*)
    [ -f ~/.zshrc.osx ] && . ~/.zshrc.osx
    ;;
# Linux
linux*)
    [ -f ~/.zshrc.linux ] && . ~/.zshrc.linux
    ;;
esac

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Pitfall

• Mac - BSD
  • or consider installing brew install gnu-sed instead

$ LANG=C find . -type f -name "*" ! -path '*/.svn/*' ! -path '*/.git/*' -print0 \
| xargs -0 sed -i '~' -e 's///gi'

• Linux - GNU

$ find . -type f -name "*" ! -path '*/.svn/*' ! -path '*/.git/*' -print0 \
| xargs -0 sed -i -e 's///gi'

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Pitfall

• Mac - BSD

$ LANG=C git ls-files -z | xargs -0 sed -i '' -e 's///gi'`

• Linux - GNU

$ git ls-files -z | xargs -0 sed -i -e 's///gi'

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Git subcommands:

$ git grep 'Could not find the specified attachment on the server'

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Release your brain resource:

• Easily navigate directories - go with fewer cds!
  • rupa/z, or
  • wting/autojump
• Remote repository management - let the tool decide where to locate the cloning repositories
  • x-motemen/ghq

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Recommended commands:

• jq
• awk
• rsync
• time
• watch

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Linter:

• koalaman/shellcheck: ShellCheck, a static analysis tool for shell scripts

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$ echo "Thank you!"

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