Shell scripts
So far, we have been running things directly on the command line, “interactively”. However, you might want to keep your commands in a file, and be able to run, share, modify, or use files as templates. This is the gateway to coding and is great practice for developing your reproducible work.
A script is a file of instructions that can be directly read and run by a program. In our case, we are going to make a script in shell language.
Let’s create a very simple script. Open nano creating a file called first_script.sh and include the lines
#!/bin/bash
ls -l *soft
echo "That is all of the files with \"soft\" in that I could find here."It is a good practice to always start your scripts with a shebang line like #!/bin/bash, that tells the system to run the correct shell for the script.
Shell scripts need to have execution permission, so it is important to remember to make your scripts executable with chmod +x script.sh. Once done it, we can run our first script with
./first_script.shVariables and structures
Scripts can also have variables, conditional structures and loops. While a deep dive into these concepts is beyond the scope of an introductory course, it is worth mentioning them to understand all the basic capabilities of shell scripting.
Use descriptive variable names:
user_name="John"
echo "Hello, ${user_name}!"Make decisions using if-then-else statements:
if [[ "$1" == "help" ]]; then
echo "Usage: script.sh [option]"
elif [[ "$1" == "version" ]]; then
echo "Version 1.0"
else
echo "Unknown option"
fiAllow repetition of commands for a specified number of iterations or over a list of items:
for file in *.txt; do
echo "Processing ${file}"
done