Ad:

Shell Scripting Discussion Thread
Unsolved
Views: 1506

May 24th, 2007

Help!need Help reading the bash script

Expand Post »

Hi..
im a newbie in shell scripting, and also new in this forum..
i understand the command below is just reading from /etc/passwd
and getting whatever in field 1 and 3 (which are username and userID)

after the cut the format will be
username:uid
my guess,its making the array with the index in respect to its userID

but i dont understand the expression
{i#*:}]=${i%: *}
could somebody please explain how to read those...
and what those will evaluate to...
and how to work with things like those(i dont think those're regex-i have no clue)..

=========================================================
for i in $(cut -f 1,3 -d: /etc/passwd) ; do array[${i#*:}]=${i%: *}done

Similar Threads

how to recursive search of subdiretories in BASH script in Shell Scripting
Bash Mail script help in Shell Scripting
HELP! Who can solve this bash script? in Shell Scripting
web page statistics - my first bash script in Shell Scripting

bergy_nj

Reputation Points: 10

Solved Threads: 0

Newbie Poster

Offline

7 posts
since May 2007

Permalink

May 29th, 2007

Re: Help!need Help reading the bash script

Shell Scripting Syntax (Toggle Plain Text)
for i in $(cut -f 1,3 -d: /etc/passwd)  
do 
  echo "${i#*:}" "${i%:*}" 
done
for i in $(cut -f 1,3 -d: /etc/passwd)  
do 
  echo "${i#*:}" "${i%:*}" 
done

This lets you see what is going on.

Shell Scripting Syntax (Toggle Plain Text)
${i#*:}
${i#*:}

is parameter substitution- returns the value just before the colon - a number that is the user id.

Shell Scripting Syntax (Toggle Plain Text)

${i%:*}

returns the username, so:
arr[number] = name

Shell Scripting Syntax (Toggle Plain Text)

${i%:*}

was changed from

Shell Scripting Syntax (Toggle Plain Text)

${i%: *}

which doesn't work, by the way.
Try man (or info) for bash or ksh. This is called parameter substitution using a POSIX shell. It finds substrings.

Last edited by jim mcnamara; May 29th, 2007 at 1:00 pm.

jim mcnamara

Reputation Points: 62

Solved Threads: 10

Junior Poster

Offline

179 posts
since May 2004

Permalink

May 29th, 2007

Re: Help!need Help reading the bash script

bash's parameter substitution is a good feature to have, but it has ugly syntax. for what you want to do, you can use awk

Shell Scripting Syntax (Toggle Plain Text)
awk -F":" '{print $3,$1}' /etc/passwd
awk -F":" '{print $3,$1}' /etc/passwd

ghostdog74

Reputation Points: 75

Solved Threads: 44

Junior Poster

Offline

156 posts
since Apr 2006

This thread is more than three months old

No one has posted to this discussion for at least three months. Please let old threads die and do not reply to them unless you feel you have something new and valuable to contribute that absolutely must be added to make the discussion complete. Otherwise, please start a new thread in this forum instead.

Previous Thread in Shell Scripting Forum Timeline: help... for LINUX/UNIX users only

Next Thread in Shell Scripting Forum Timeline: Swaping Files

DaniWeb Message

Cancel Changes

User Name
Password