The document discusses best practices for using the command line interface (CLI) efficiently. It provides examples of using common UNIX commands like grep, find, awk, sort, uniq, and xargs to analyze command history, filter output, run commands in parallel, and handle encoding. The document emphasizes building small, focused tools according to the UNIX philosophy and provides tips for common tasks like capturing command output, checking exit statuses, running subprocesses, and handling different operating systems. Recommendations are made for CLI productivity tools and the linter ShellCheck.

1. The Art of Command Line
2021-02-22
Kenta Yamamoto (@i05)
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2. Unix Philosophy - "The Art of UNIX Programming" (2003)
2

3. $ 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
Make each program do one thing well. To do a new job, build
afresh rather than complicate old programs by adding new
features.
“
“
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4. 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
4

5. 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
5

6. 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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7. 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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8. 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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9. Subroutine - $(command)
$ curl "https://jpnic.rdap.apnic.net/ip/$(dig +short myip.opendns.com @resolver1.opendns.com)"
| jq .
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10. 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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11. Multibyte encoding - nkf :
$ find . -type f -name "*.txt" | xargs nkf --guess
$ find . -type f -print0 | xargs -0 nkf --overwrite -w
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12. Multiline:
TEXT_LIST=$(cat << EOF
__HERE_DOCUMENT__
__HERE_DOCUMENT__
EOF
)
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13. Runs everywhere:
case "${OSTYPE}" in
# Mac
darwin*)
[ -f ~/.zshrc.osx ] && . ~/.zshrc.osx
;;
# Linux
linux*)
[ -f ~/.zshrc.linux ] && . ~/.zshrc.linux
;;
esac
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14. 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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15. 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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16. Git subcommands:
$ git grep 'Could not find the specified attachment on the server'
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17. Release your brain resource:
Easily navigate directories - go with fewer cd s!
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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18. Recommended commands:
jq
awk
rsync
time
watch
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19. Linter:
koalaman/shellcheck: ShellCheck, a static analysis tool for shell
scripts
19

20. $ echo "Thank you!"
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21. 21