Shell

Shell#

date:

2020-12-26

version:

1

String#

Get length:

${#str}

Substring / Slice:

${str:1:4}

Replace:

${v%.md}.rst

Prefix & Subfix:

${foo#"$prefix"}
${foo%"$suffix"}

Heredoc#

Syntax:

cat <<EOF
... Heredoc content
EOF

备注

Shell variables in heredoc will be expanded

Avoid shell expanding variables:

cat <<'EOF'
... Heredoc ${content}
EOF

Write to file:

cat << EOF > /tmp/foo
... Heredoc content
EOF

Output to variable, 使用时需要 quote 以保持原格式 "$VAR":

read -r -d '' VAR << EOF
... Heredoc content
EOF

参见

How can I assign a heredoc value to a variable in Bash? - Stack Overflow

<<-EOF will ignore leading tabs in your heredoc, while <<EOF will not.

Command Line Arguments#

Number of pass-in arguments:

$#

The "pass-in argument list:

$* # Default, an *string*
$@ # Default, a *array*

The arguments of previous command:

!^      # First one
!$      # Last one
!*      # All
!:n     # N-th
!:n-m   # Range n~m

Command Line Wrapper 模版#

#!/bin/bash

EXEC="xxxx"

exec $EXEC $*

Bash set options#

Get help:

$ bash -c 'help set'

脚本常用参数：

-e:

Exit immediately if a command exits with a non-zero status.

-x:

Print commands and their arguments as they are executed.

-u:

Treat unset variables as an error when substituting.

数组#

Access by index:

arr=("one" "tow" "three")
for i in ${!arr[@]}; do
    echo $i ${arr[i]}
done

交互式数组#

查看行编辑快捷键:

$ bindkey -M

Switch Case#

case word in
   pattern1)
      Statement(s) to be executed if pattern1 matches
      ;;
   pattern2)
      Statement(s) to be executed if pattern2 matches
      ;;
   pattern3)
      Statement(s) to be executed if pattern3 matches
      ;;
   *)
     Default condition to be executed
     ;;
esac
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