Shell Programming and Scripting

Hi,
I have a requirement to extract a variable string (say S1) from a given file (say File-A), and look for a certain pattern to find another string (say S2) in another file (say File-B) and replace S2 with S1.

An example could be:
You have got two password shadow files -
1) shadow1
2) shadow2

These files are colon (":") seperated fields (like any "/etc/shadow" file has).
I now need to look for a user (say 'David'); user entry is the first field in both the shadow files (both of the shadow files are having multiple users along with the user 'David') and replace the second field in the shadow files (which is the actual encrypted password string) of file 'shadow1' with the corressponding field in file 'shadow2' for the user 'David.

Password strings could be of any lengths and may contain all kinds of possible characters.

An example of AWK/gawk script would be the most desired on which can be embedded/called from a bash script.

However any method of solving this problem using Linux bash will do well for me.

Thank you very much in advance.

Please provide a sample of input files and desired output.

my understanding about ur requirement is ...you are looking up the value from password file and matching with it on a different column...

awk -F":" 'NR==FNR{a[$1]=$2; next} NR!=FNR{if(a[$1])print $1," ",a[$1]; else print $0 }' file2 file1

this will list all the values of file1...

Thank you very much for your response.
However, somehow I received a syntax error at the position of 'else'.

am sorry i dint get the error...
can you please give the complete error...
for the time being can you just try the following code

Code:

awk -F":" 'NR==FNR{a[$1]=$2; next} NR!=FNR{if(a[$1])print $1," ",a[$1]; }' file2 file1

Is it possible you left out the ; before the else? That would give a syntax error.

hi vi,

Code:

awk -F":" 'NR==FNR{a[$1]=$2; next} NR!=FNR{if(a[$1])print $1," ",a[$1]; else print $0 }' file2 file1

which semicolon you are pointing to...i dint get you ???
i hav executed this command and it is working fine for me...
file1:

Code:

abc: 123
def: 456
ghi: pwd3

file2:

Code:

sam: ddd
def: pwd2
ram: mbo
abc: pwd1

O/P:

Code:

abc  pwd1
def   pwd2

hope this solves your problem

@vi_curious i think you are new to scripting i guess semicolon( always means enter or new line so that shouldnt be a prob...