查看GNU/Linux Tips的源代码

== Bash ==

=== 命令行参数 ===

<source lang=bash>
#!/bin/bash

CUR_YMD=$(date +%Y%m%d)

# Example: 706
M=$1

if [ $# -le 0 ]; then
    M=$CUR_YMD
else
    M=$((M+20250000))
fi

echo "| $M: "
</source>

<br>

=== sort ===

* https://www.cnblogs.com/51linux/archive/2012/05/23/2515299.html

<br>

=== if ===

* -e checks if a file or directory exists, regardless of its type
* -f checks if the path exists and refers to a regular file (not a directory, symbolic link, etc.)
* -d checks if the path exists and refers to a directory

<source lang=bash>
FILE="/path/to/your/file.txt"
if [ -e "$FILE" ]; then
  echo "File exists."
else
  echo "File does not exist."
fi
</source>

=== While ===

<source lang=bash>
while [[ $snum -le $enum ]];  
do  
echo $snum  
((snum++))  
done
</source>

<br>
=== For ===

<source lang=bash>
DIDS="
121
122
123
124
125
"

for d in $DIDS; do echo $d; done
</source>

=== Bell ===

<source lang=bash>
echo -en "\007"
</source>

<br>

=== Random Num ===

<source lang=bash>
RANDOM := $(shell od -An -N2 -i /dev/random | tr -d ' ')

##############################################
RANDOM := $(shell /bin/bash -c 'echo $$RANDOM')

test:
    echo $(RANDOM)

##############################################
awk 'BEGIN{srand();printf("%d", 65536*rand())}'
</source>

<br>

=== Notes ===

<source lang=bash>
$ set -- one two
$ echo $1
one
$ echo ${1}
1
$ eval echo ${1}
one

$ n=2
$ echo ${n}
2
$ echo ${!n}
two
$ eval echo \${$n}
two
</source>

'''String:'''

<source lang=bash>
text=${text/ /-}     # 只替换一个空格
text=${text// /-}    # 全部替换空格

$ cat test.txt |tr -s [:space:]

echo ${var^}      # 把变量中的第一个字符换成大写 
echo ${var^^}    # 把变量中的所有小写字母，全部替换为大写
echo ${var,}       # 把变量中的第一个字符换成小写
echo ${var,,}      # 把变量中的所有大写字母，全部替换为小写
</source>

<br><br>

=== Bash readline ===

<source lang=bash>
#!/bin/bash 
count=1
cat X1A001.dat | while read line        # 从文本文件 X1A001.dat 一行一行的读 
do 
   echo "$count:$line" 
   count=$(($count + 1))
done
exit 0
</source>

<br><br>

=== 命令行历史 ===

;;1. 忽略当前这条命令

  $ export HISTCONTROL=ignorespace
  $ [space]echo "this is a top secret"


;;2. 禁用当前会话的所有历史记录

  $ export HISTSIZE=0


;;3. 工作结束后清除整个历史

  $ history -cw


;;4. 只针对你的工作关闭历史记录

  $ [space]set +o history
 
要重新开启:

  $ [space]set -o history


;;5. 从历史记录中删除指定的命令

  $ history
  $ history -d 3

<br><br>