This script will iterate over a file and echo out every single line:
#!/bin/bash
​
for line in $(cat file.txt);do
echo $line
done
Another way of writing is this:
#!/bin/bash
​
while read p; do
echo $p
done <file.txt
For-loops
#!/bin/bash
​
for ((i = 0; i < 10; i++)); do
echo $i
done
Another way to write this is by using the program seq. Seq is pretty much like range() in python. So it can be used like this:
#!/bin/bash
​
for x in `seq 1 100`; do
echo $x
done
If statement
$1 here represent the first argument.
​
if [ "$1" == "" ]; then
echo "This happens"
fi
If/Else
#!/bin/bash
​
if [ "$1" == "" ]; then
echo "This happens"
else
echo "Something else happens"
fi
Command line arguments
Command line arguments are represented like this
#!/bin/bash
​
$1
This is the first command line argument.
Daemonize an execution
If you do a ping-sweep with host the command will take about a second to complete. And if you run that against 255 hosts I will take a long time to complete. To avoid this we can just deamonize every execution to make it faster. We use the & to daemonize it.
#!/bin/bash
​
for ip in $(cat ips.txt); do
ping -c 1 $ip &
done
Use the output of command
It has happened to me several times that I want to input the output of a command into a new command, for example:
I search for a file, find three, and take the last line, which is a path. Now I want to cat that path: