Shell FAQ

skip first n line

tail -n +1

sort in place

# -o 可以，不要 > file
sort -o file{,}

tree utf8 chartset

# -N Print non-printable characters
tree -N

tree exclude

tree -I 'containerd|docker'
tree -I 'node_modules|cache|test_*'

tree -L 3 -I 'node_modules*|cache*'

shebang

for bash

#!/usr/bin/env bash

posix shell

#!/bin/sh

获取一个 Tab 字符

echo -ne \\t | pbcopy

找到最大的文件

find . -printf '%s %p\n' | sort -nr | head
find . -maxdepth 1 -printf '%s %p\n' | sort -nr | head
du -a . | sort -nr | head

文件时间信息

touch file
stat file
TZ=UTC stat -c '%y %n' file
date -r file +%s
# [[CC]YY]MMDDhhmm[.ss]
touch -a -m -t 203801181205.09 file
touch -d "2012-10-19 12:12:12.000000000 +0530" file

crtime - birt time

inode=$(stat -c %i test)
# stat 信息
debugfs -R "stat ${inode}" /dev/sdb1
# 危险操作
umount /dev/sdb1
debugfs -w -R "set_inode_field ${inode} crtime 200001010101.11" /dev/sdb1

• herzbube/birthtime_touch

pwd vs cwd

type -a pwd

-	-
builtin pwd	echo $PWD
/bin/pwd	pwd -P
getcwd	readlink -f /proc/self/cwd

doas vs sudo

• doas
  • 95% of the features of sudo with a fraction of the codebase
  • ~1000 LOC
• sudo
  • ~18K LOC
  • 依赖很多 - eventlog, iolog, logsrv, protobuf-c, zlib
  • logsrvd
  • 功能多一些 - 不一定会用得到

string include/match

[[ 'abcd' = *'bc'* ]] && echo yes
[[ 'abcd' =~ 'bc' ]] && echo yes
str=abcd [ -z "${str##*bc*}" ] && echo yes

trim space

echo "   lol  " | xargs
# 不会 trim 换行
echo -e "   lol\r\n  " | xargs | hexdump -C
# 移除所有空白
echo -e 'a b c\r' | tr -d '[:space:]'
# trim left - sed 不能替换 \r\n
echo -e ' \r\nabc\r\n ' | sed -e 's/^[[:space:]]*//'
# trim right
echo -e ' abc ' | sed -e 's/[[:space:]]*$//'

Terminal vs Console vs Shell

• console = physical terminal
  • 物理实体
• terminal = tty = teletype = text input/output environment
  • 链路协议接口
• shell = command line interpreter
  • 上层抽象行为概念
  • 逻辑协议

基于时间搜索

# 修改时间在某个时间点之前的目录
find . -maxdepth 1 -type d -not -newermt 2022-01-01 -ls
# 递归删除
find . -maxdepth 1 -type d -not -newermt 2022-01-01 -exec rm -r {} ';'

修复一般文件和目录 mod

find . -type d -exec chmod 0755 {} \;
find . -type f -exec chmod 0644 {} \;

# 修复 某个 owner
find . -type d -user harry -exec chown daisy {} \;

shell vs python

• shell - 必知必会
  • 让简单的事情 非常简单，让复杂的事情 非常复杂
  • 复杂过后可维护性差
  • 核心优势在于 compose/组合/联结 各种工具
  • 环境可预期
  • 但 工具 不一定完全兼容
    • posix/gnu/busybox/coreutils/findutils/util-linux
• python - 补充扩展
  • 难度适中，可维护
  • 目前大多 linux 环境都有安装 python
  • python 也是 shell 一部分

---

• https://stackoverflow.com/q/796319/1870054

zsh vs bash

vs.	zsh	bash
interactive shell	.zshrc	.inputrc,.bashrc
login shell	.zprofile	.profile,.bash_profile
key binding	bindkey -> zle	.inputrc bind -> readline
prompt PS1 escape	PS1 - % 转义	PS1 - ``` 转义
promot command	precmd + preexec hook	PROMPT_COMMAND
array index	start from 1	start from 0

• zsh
  • 多用于用户环境
    • 交互更好
    • 功能更多
• bash
  • 多用于服务端环境
    • 默认
    • 稳定

---

• https://apple.stackexchange.com/a/361957/103557

tee stderr

echo message | tee -a /dev/fd/2 > /dev/null

Sort Large File

split -l 1000000 in.txt chunk
for X in chunk*; do sort < $X > sorted-$X; done
sort -m sorted-chunk* > out.txt

# 清理
rm chunk* sorted-chunk*

• -m 只合并不做整体排序
• --parallel=$(nproc) 并行
• https://man7.org/linux/man-pages/man1/sort.1.html

arch

architecture=""
case $(uname -m) in
  i386 | i686) architecture="386" ;;
  x86_64) architecture="amd64" ;;
  # apk --print-arch
  arm) dpkg --print-architecture | grep -q "arm64" && architecture="arm64" || architecture="arm" ;;
esac

detect

if [ -n "$ZSH_VERSION" ]; then
  echo "zsh"
elif [ -n "$BASH_VERSION" ]; then
  echo "bash"
else
  # assume something else
fi

case $SHELL in
  */zsh)
    echo "zsh"
    ;;
  */bash)
    echo "bash"
    ;;
  *) ;;
    # assume something else
esac

• FCEDIT
  • fcsh
• KSH_VERSION
  • ksh
• PS3
  • ps3sh

PATH

• /etc/paths
• /etc/paths.d

macOS

• /usr/libexec/path_helper

/usr/local/bin
/System/Cryptexes/App/usr/bin
/usr/bin
/bin
/usr/sbin
/sbin

/etc/paths.d/10-cryptex

/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin
/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin
/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin