Scripting. More Shell Scripts Loops. Adapted from Practical Unix and Programming Hunter College

Transcription

1 Scripting More Shell Scripts Loops Adapted from Practical Unix and Programming Hunter College Copyright Stewart Weiss

2 Loops: for The for script version 1: 1 #!/bin/bash 2 for i in do 4 echo $i 5 done Line numbers are part of the editor, not the script! 2 Comp 190 Scripting Languages

3 Loops: for The for script version 2: 1 #!/bin/bash 2 for file in temp1.txt temp2.txt temp3.txt 3 do 4 more $file 5 done Write a script that removes all lines containing the word "October" from the three files. 3 Comp 190 Scripting Languages

4 Loops: for The for script version 2: 1 #!/bin/bash 2 for file in temp1.txt temp2.txt temp3.txt 3 do 4 grep -v "October" $file > tempfile 5 mv tempfile $file 6 done Change your script to read the search word from the command line. 4 Comp 190 Scripting Languages

5 Loops: for The for script version 3 (using regex): 1 #!/bin/bash 2 for file in temp[1-3].txt 3 do 4 grep -v "October" $file > tempfile 5 mv tempfile $file 6 done The shell permits filename substitution 5 Comp 190 Scripting Languages

6 Loops: for The for script version 4: 1 #!/bin/bash 2 for file in * 3 do 4 grep -v "October" $file > tempfile 5 mv tempfile $file 6 done This would remove the word "October" from ALL files in the directory. 6 Comp 190 Scripting Languages

7 Loops: for The for script version 5: 1 #!/bin/bash 2 files=$(cat filelist) 3 for file in $files 4 do 5 grep -v "October" $file > tempfile 6 mv tempfile $file 7 done This would remove the word "October" from the files whose name is contained in the file "filelist". 7 Comp 190 Scripting Languages

8 Loops: for The for script version 6: 1 #!/bin/bash 2 # delete "October" lines from all files on the command line 3 # $* contains all command line parameters 4 for file in $* 5 do 6 grep -v "October" $file > tempfile 7 mv tempfile $file 8 done This would remove the word "October" from ALL files listed on the command line. 8 Comp 190 Scripting Languages

9 Loops: for The for script version 7: 1 #!/bin/bash 2 # echo comand line args 3 # $* contains all command line parameters 4 for arg in $* 5 do 6 echo $arg 7 done Try this with command line args: args a b c # where 'args' is the script name args 'a b' c # $* is replaced by the shell with # a b c and the quotes are lost! 9 Comp 190 Scripting Languages

10 Loops: for The for script version 8: 1 #!/bin/bash 2 # echo comand line args 3 # $@ contains all command line parameters 4 for arg in $@ 5 do 6 echo $arg 7 done Try this with command line args: args a b c # where 'args' is the script name args 'a b' c # $@ quotes each arg, so "a b" "c" 10 Comp 190 Scripting Languages

11 Loops breaking out of loops: 1 while true 2 do 3 cmd=$(getcmd) 4 5 if [ "$cmd" = quit ] 6 then 7 break 8 else 9 echo "$cmd" 10 fi 11 done break n will break out of the n innermost loops 11 Comp 190 Scripting Languages

12 Loops continuing loops: for file in $* do if [! -e "$file" ] then echo "$file not found!" continue fi # process file 12 Comp 190 Scripting Languages

13 Loops I/O redirection on a loop: for i in do echo $i done > loopout puts the output of the loop into the file "loopout" 13 Comp 190 Scripting Languages

14 Loops Overridding I/O redirection on a loop: for i in do echo $i > /dev/tty done > loopout /dev/tty is the terminal. This script explicitly sends output to the terminal. 14 Comp 190 Scripting Languages

15 Loops I/O redirection on standard error: for i in do echo $i done 2> errors 2> redirects stderr not stdout 15 Comp 190 Scripting Languages

16 Loops piping: for i in do echo $i done wc -l pipe output to the wordcount program This prints out "4" 16 Comp 190 Scripting Languages

17 && and constructs in the shell &&: command1 && command2 command1 is always executed if command1 returns an exit status of zero (success) then command2 is executed. otherwise, command2 is NOT executed sort bigdata > /tmp/sortout && mv /tmp/sortout bigdata only executes the mv command if the sort was successful [ -z "$EDITOR" ] && EDITOR=/bin/ed tests the value of the variable EDITOR. If it's null, /bin/ed is assigned to it. 17 Comp 190 Scripting Languages

18 && and constructs in the shell : command1 command2 command1 is always executed if command1 returns an exit status of nonzero (failure) then command2 is executed. otherwise, command2 is NOT executed grep "$name" phonebook echo "Couldn't find $name" only do the echo if grep doesn't find the name in the phonebook or can't open phonebook 18 Comp 190 Scripting Languages

19 && and constructs in the shell complex commands: command1 command2 You can use a complex sequence of commands on either or both left or right side of a && or construct. who grep "^$name > /dev/null echo "$name's not logged on" causes exxecution of the echo if the grep fails see the textbook for more complex examples 19 Comp 190 Scripting Languages

20 Things to try Try creating a few simple scripts of your own. It will give you practice using gedit if you are at a UNIX console, or vi or nano if you are not. Read about the test command and learn its tricky syntax. Play around with > to store the output of various commands. 20 Comp 190 Scripting Languages