create_simple_shell_script.md

Creating a Shell Script to Create New Shell Scripts Based on a Template

For this example, I am creating a shell script to create another shell script that prints a specific message based on a template.

Template File Name : script-XXX.template

Content of the Template:

#!/bin/sh
# Simple Shell Script to Greet 
echo Hello, XXX

XXX is the placeholder for replacement

Script File Name : scripter.sh

1. Create a simple script file and test. Start with the shebang and echo Hello (TDD)

#!/bin/sh
echo Hello

2. Set permision to script chmod

chmod 755 scripter.sh

3. Execute script and verify it's functioning

>./scripter.sh
Hello

4. In scripter.sh remove the echo Hello line and replace it with a

• variable to hold file name
• take a copy of template with file name (cp)
• set permision to execute it

#!/bin/sh
fileName=say-$1.sh
cp script-XXX.template $fileName
chmod 755 $fileName

5. Use SED to replace place holder with desired value, in this case it's the same parameter

#!/bin/sh
fileName=say-$1.sh
cp script-XXX.template $fileName
chmod 755 $fileName

sed -i 's/XXX/'$1'/g' $fileName

6. Now the script is complete. you can execute to create say-World.sh file and executes it.

>./scripter.sh World.sh
>./World.sh

Even though this will do the needful we can improve it little more

• Keep the template inside the scripter.sh itself by padding required lines in the output with some hashes(single hash marks line as comment) e.g. ###. Then we can read them using grep ( grep '###' ). This will read the line itself but with tail we can skip this ( tail -n +2 ) ( with $0 script can read it's name and $1-9 are command arguments)
• By checking the file exists we can avoid replacing existing files ( if [ -f $fileName ] )
• We can inline SED
• Fold lines if they are too long (only in console output)
• Then add nl to find line numbers

Final Script:

#!/bin/sh
fileName=say-$1.sh

if [ -f $fileName ]
then
  echo
  echo ------------------------------------------------------------------------------------
  echo  $fileName Exist if you want to replace it please delete the before executing this.
  echo ------------------------------------------------------------------------------------
  echo
  exit 1
fi

echo --------------------------------------
echo Creating File : $fileName
echo --------------------------------------
echo Content:
echo --------------------------------------
grep '### ' $0 | sed 's/XXX/'$1'/g;s/### //g' | tail -n +2 | tee -a  $fileName | nl | fold -w 100 -s
echo --------------------------------------

chmod 755 $fileName
echo
echo --------------------------------------
echo $fileName Created!
echo --------------------------------------
echo

### #!/bin/sh
### # Simple Shell Script to Greet 
### echo Hello, XXX

• Comprehensive Tutorial on Shell Scripting https://www.shellscript.sh/