The following are ten examples of Linux for loop using bash shell scripting.
1. Iterate between a range of numbers
#!/bin/bash
for nvar in {1..10}
do
echo $nvar
doneOutput
1 2 3 4 5 6 7 8 9 10
2. Loop until reach given value
#!/bin/bash nmax=10 for ((i=1; i<=nmax; i++)) do echo -n "$i " done
Output
1 2 3 4 5 6 7 8 9 10 $
3. Loop through a specific range of numbers hardcoded
#!/bin/bash for nvar in 11 12 13 14 15 16 17 18 19 20 do echo $nvar done
4. Loop and print all the parameters passed to the script
#!/bin/sh for nvar in $* do echo "Parameter contains: $nvar" done
Test
./for4.sh one two three
Output
Parameter contains: one Parameter contains: two Parameter contains: three
5. Read a text file word by word
#!/bin/bash # create a text file named textfile.txt and put some content # India Singapore Hong Kong United Kingdom for cvar in `cat textfile.txt` do echo "cvar contains: $cvar" done
Output
cvar contains: India cvar contains: Singapore cvar contains: Hong cvar contains: Kong cvar contains: United cvar contains: Kingdom
6. Read the contents of a directory
#!/bin/bash echo -n "Contents of the directory are : $var" for var in $(ls ./*) do echo "$var" done
Output
./album.sh ./busy.sh ./calc.sh
7. Read a list of files to make a backup copy
#!/bin/bash for filename in *.sh do echo "Copying $filename to $filename.bak" cp $filename $filename.bak done
8. Loop with Continue statement
#!/bin/bash for var in 1 2 3 do echo before $var continue echo after $var done exit 0
Output
before 1 before 2 before 3
9. Ask for input to display the square of a number until 0
#!/bin/bash typeset -i num=0 while true do echo -n "Enter any number (0 to exit): " read num junk if (( num == 0 )) then break else echo "Square of $num is $(( num * num ))." fi done echo "script has ended"
Output
Enter any number (0 to exit): 8 Square of 8 is 64. Enter any number (0 to exit): 15 Square of 15 is 225. Enter any number (0 to exit): 6 Square of 6 is 36. Enter any number (0 to exit): 0 script has ended
10. Loop for specified number values with sorting
#!/bin/bash for value in 9 3 17 22 15 23 do echo $value done | sort -n
Output
3 9 15 17 22 23
