Bash problem

Shell Programming and Scripting
1

Hello there, I'm a beginner in bash programining and I have a problem with the interpretetion of the code: sed -e "s/\([^:]*\):.*/\1/" in this for loop:

for process in $(sed -e "s/\([^:]*\):.*/\1/" /etc/passwd)

thx for any help

edgehead

2

The sed statement returns the first field \1 or group of characters that is not a :
In other words the : acts a as a field separator. The first field of /etc/passwd is the username.

So
"for process in first field name of all records in /etc/passwd" is a start of a for loop that reads thru the passwd file, that sets the process variable equal to each of the usernames in the passwd file, in turn.

3

thanks Jeff for the fast reply I did not expect it so fast:)
I get it for this example but is there a manual for all of the tokens in the " " for this sed function?

I have another problem. I have written a program which prints me the latest changed file in the directory and his subdirectories but i get a error and i don't know why!
Here is the code:

#!/bin/bash 
#Check for number of parametersd 
if [ $# -ne 1 ]; then 
  echo "USAGE: $0 path" 
  exit 0 
fi 
#Go through all directories 
for directory in $`ls $1 -R | grep -e ":$" | sed -e "s/://g"` do 
  line=0 
  filename="" 
  fileinfo="" 
  #Get information for the file that was most recently modified 
  for entry in $(ls $directory -lt | grep -e "-"); do 
    if [ $line -gt 8 ]; then  
      break 
    fi 
    if [ $line -gt 4 ]; then 
      if [ $line -lt 8 ]; then 
        fileinfo="$fileinfo $entry" 
      fi 
    fi 
    if [ $line -eq 8 ]; then 
      filename=$entry 
    fi 
    let line=line+1 
  done 
  if [ "$filename" != "" ]; then 
    s=`find $1 -newer $directory/$filename` 
    if [ "$s" = "" ]; then 
      echo "$directory/$filename $fileinfo" 
      exit 0 
    fi 
  fi 
done 
echo "No files found."

thanks for the help

edgehead

4

Search google for Sed tutorial or regular expressions, you'll get many free tutorials.