Linux - How to write and execute Linux Shell scripts

shell script

shell script

To put it simply, a shell script expresses the each of the commands in the command line in Linux as a kind of file, and when the file is executed, it gives the effect that the commands were executed at just one command line.

Shell script characteristics

• It is not compiled but interpreted by the operating system.
• There are many types of shell scripts. (sh, dash, bash, rbash) What we’re going to cover in this post is bash scripts.
• bash : rebuilt the existing basic shell
  • It is currently most widely used in linux-based operating systems.
  • When writing a bash script #! /bin/bash You can see that it starts like this, and it means the type of shell script.

Loop

• example

#!/bin/bash

while [ $n -le 10 ] # (( $n <= 10 ))
do
    echo $n
    (( n++ )) #$(( n+1 ))
done

Example in steps

Edit mode after creating a shell file

• vi [shell file name]

$ vi atest_100

atest_100

• line 1 : #!/bin/bash

#!/bin/sh

int=0
while test "$int" -lt "100"

do
  a module --force
  int=`expr $int + 1`
done

Grant permission to execute shell file

• ls -al : -rw-r–r– –> -rwxr-xr-x

$ chmod 755 atest_100

Execute Shell script

- ./ atest_100
- sh atest_100
- bash atest_100
- run test 100 times

$ sh atest_100