Bourne Shell Looping

for loop

The for loop has the following construct:

for variable in words do command ... done

Script Output

$ cat bl1 for i in 1 2 3 4 5 6 do echo $i done

$ bl1 1 2 3 4 5 6

$ cat bl2 for i in `date` do echo $i done

$ bl2 Fri Mar 16 10:05:18 CST 2001

If the list of words is omitted, then the list of words is the command line arguments.
$ cat bl6 for i do echo $i done

$ bl6 1 '2 3' 4 1 2 3 4

Script	Output
$ cat bl1 for i in 1 2 3 4 5 6 do echo $i done	$ bl1 1 2 3 4 5 6
$ cat bl2 for i in `date` do echo $i done	$ bl2 Fri Mar 16 10:05:18 CST 2001
If the list of words is omitted, then the list of words is the command line arguments. $ cat bl6 for i do echo $i done	$ bl6 1 '2 3' 4 1 2 3 4

while loop.

The while construct is :

while command do command ... done

Script Output

$ cat bl5 while [ $# -gt 0 ] do echo $1 shift done

$ bl5 1 2 '3 4' 5 1 2 3 4 5

Script	Output
$ cat bl5 while [ $# -gt 0 ] do echo $1 shift done	$ bl5 1 2 '3 4' 5 1 2 3 4 5

until loop.

The until looping construct is:

until command do command ... done

Script Output

$ cat bl7 until [ $# -eq 0 ] do echo $1 shift done

$ bl7 123 456 789 123 456 789

Script	Output
$ cat bl7 until [ $# -eq 0 ] do echo $1 shift done	$ bl7 123 456 789 123 456 789

Examples

A couple of examples are:

Directory list.

List the subdirectories in a directory.

Script Output

$ cat bl8 rpath=$1 files=`ls $1` for entry in $files do if [ -d $rpath/$entry ] then echo $rpath/$entry fi done

$ bl8 Mail Mail/drafts Mail/inbox $ bl8 c c/acctng c/class c/fmt c/obfuscated c/rid c/utility

To list directories down in the tree make the script recursive:

Script	Output
$ cat bl8 rpath=$1 files=`ls $1` for entry in $files do if [ -d $rpath/$entry ] then echo $rpath/$entry fi done	$ bl8 Mail Mail/drafts Mail/inbox $ bl8 c c/acctng c/class c/fmt c/obfuscated c/rid c/utility

Script

#!/bin/sh
rpath=$1
files=`ls  $1`
for enrty in $files
do
  if [ -d $rpath/$entry ]
  then
     echo $rpath/$entry
     ./bl8 $rpath/$entry        
  fi
done

Output of recurrsive script

$./bl8 Satan
Satan/satan-1.1.1
Satan/satan-1.1.1/bin
Satan/satan-1.1.1/config
Satan/satan-1.1.1/html
Satan/satan-1.1.1/html/tutorials
Satan/satan-1.1.1/html/tutorials/first_time
Satan/satan-1.1.1/html/tutorials/vulnerability
Satan/satan-1.1.1/include
Satan/satan-1.1.1/include/netinet

Multiple occurance of a program

Run multiple occurrences of a program on different files.

$ ls /home/kochis/Accounting/Cpr/Wip
dripro.d        marinevirus.d   molemodlbile.d  speedup.d
maglevtexmap.d  molecardimed.d  sematech.d      uthscsaphy.d

Script

$ cat apply
#!/bin/sh
for file
do
   sansd=`echo $file | sed 's/\.d//'`
   echo 1 : $sansd
   key=`echo $sansd | sed 's/^.*\///'`
   echo 2 : $key
   echo 3 : dbtext wd $key $file
   echo
done

Output

$ apply /home/kochis/Accounting/Cpr/Wip/*.d
1 : /home/kochis/Accounting/Cpr/Wip/dripro
2 : dripro
3 : dbtext wd dripro /home/kochis/Accounting/Cpr/Wip/dripro.d

1 : /home/kochis/Accounting/Cpr/Wip/maglevtexmap
2 : maglevtexmap
3 : dbtext wd maglevtexmap /home/kochis/Accounting/Cpr/Wip/maglevtexmap.d

1 : /home/kochis/Accounting/Cpr/Wip/marinevirus
2 : marinevirus
3 : dbtext wd marinevirus /home/kochis/Accounting/Cpr/Wip/marinevirus.d

1 : /home/kochis/Accounting/Cpr/Wip/molecardimed
2 : molecardimed
3 : dbtext wd molecardimed /home/kochis/Accounting/Cpr/Wip/molecardimed.d

1 : /home/kochis/Accounting/Cpr/Wip/molemodlbile
2 : molemodlbile
3 : dbtext wd molemodlbile /home/kochis/Accounting/Cpr/Wip/molemodlbile.d

1 : /home/kochis/Accounting/Cpr/Wip/sematech
2 : sematech
3 : dbtext wd sematech /home/kochis/Accounting/Cpr/Wip/sematech.d

1 : /home/kochis/Accounting/Cpr/Wip/speedup
2 : speedup
3 : dbtext wd speedup /home/kochis/Accounting/Cpr/Wip/speedup.d

1 : /home/kochis/Accounting/Cpr/Wip/uthscsaphy
2 : uthscsaphy
3 : dbtext wd uthscsaphy /home/kochis/Accounting/Cpr/Wip/uthscsaphy.d

Sum bytes in a directory

$ ls -l
total 32
-rw-r--r--   1 ask      staff         39 Jun 29 08:59 bl2
-rwxr-xr-x   1 ask      staff        151 Jun 29 09:04 bsum
-rwxr-xr-x   1 ask      staff         25 Oct 21 1997  testa
-rwxr-xr-x   1 ask      staff         80 Oct 21 1997  testb

$ ls -s
total 16       4 bl2       4 bsum      4 testa     4 testb

Script

$ cat bsum
#!/bin/sh
bytes=`ls -l | tr -s ' ' ':' | cut -d: -f5`
total=0
for count  in $bytes
do
 total=`expr $total + $count`
done
echo there are $total bytes in this directory

Output of sum script

$ bsum
there are 295 bytes in this directory

For debugging use the -x option.

Ouptut of sum script with trace on

$ sh -x bsum
+ ls -l
+ tr -s   :
+ cut -d: -f5
bytes=
39
151
25
80
total=0
+ expr 0 + 39
total=39
+ expr 39 + 151
total=190
+ expr 190 + 25
total=215
+ expr 215 + 80
total=295
+ echo there are 295 bytes in this directory

Last revision 10/17/2001