difference between `sh` and `source`

https://stackoverflow.com/questions/13786499/what-is-the-difference-between-sh-and-source

When you call source (or its alias .), you insert the script in the current bash process. So you could read variables set by the script.

When you call sh, you initiate a fork (sub-process) that runs a new session of /bin/sh, which is usually a symbolic link to bash. In this case, environment variables set by the sub-script would be dropped when the sub-script finishes.

run script

nohup python -u myscript.py > myout.file 2>&1 &

stderr stdout

• stderr/stdout分别输出到文件

  python test.py 2>stderr.log 1>stdout.log
  

• stderr/stdout分别输出到文件，也打印到屏幕

  # -a 代表append
  python test.py 2> >(tee -a stderr.log) 1> >(tee -a stdout.log)
  

进程

• 获取上一个进程号

  echo $!
  

• 获取上一个command的退出码

  # 经测试，获得的是当前session的上一个命令的退出码，如果开两个窗口，之间互不干扰
  # cmd1 | cmd2 会返回cmd2的退出码
  # cmd & 总是会返回0
  echo $?
  

• 后台执行获取退出码

  python -c 'import time; time.sleep(10); a = b'
  wait $!
  echo $?
  # 这时就会返回这个python命令的退出码，exit_code=1
  

调试shell

https://www.ibm.com/developerworks/cn/linux/l-cn-shell-debug/index.html

Syntax

• sh file head

#!bin/sh
set -e -u -x
export LANG=en_US.UTF-8

# -e Exit immediately if a command exits with a non-zero status.
# -u Treat unset variables as an error when substituting.
# -x Print commands and their arguments as they are executed.

• for

# for int range
for i in {1..100}
do
    echo $i
done

# for int range use seq
for i in $(seq $start $end); do echo $i; done

• xagrs

# -I
seq 1 30 | xargs -I {} date -d "2018/11/{}" "+%Y-%m-%d"

• strip

${string#substring}Strip shortest match of $substring from front of $string
${string%substring}Strip shortest match of $substring from back of $string
#代表删除从前往后最小匹配的内容
%代表删除从后往前最小匹配的内容

s="abc"
${s#a} # -> bc
${s%c} # -> ab

s="a/b/c"
${s#*/} # -> b/c
${s%/*} # -> a/b

• path parse

p="./foo/bar/f.txt"
echo `dirname $p` # -> ./foo/bar
echo `basename $p` # -> f.txt

Topic

loop date range

sdate=20190101
edate=20190110

idate="$sdate"
while [[ ! "$idate" > "$edate" ]]; do
  echo $idate
  idate=$(date -d "$idate +1 day" +%Y%m%d)
done