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Insert new pattern in newline after the nth occurrence of a line pattern - Bash in Ubuntu 12.04

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Top Forums Shell Programming and Scripting Insert new pattern in newline after the nth occurrence of a line pattern - Bash in Ubuntu 12.04
# 8  
Old 09-13-2012
In that case, try:
Code:
awk '$0~"^[ \t]*"patt"[ \t]*$"{which++;if(which==n)$0=$0 RS repl}1' patt="$pattern" repl="$new_pattern" n=$n data.db

No need to provide for spaces/tabs before/after the pattern.
This User Gave Thanks to elixir_sinari For This Post:
Phil3759
# 9  
Old 09-13-2012
data.db
Code:
on post-fs-data
    # We chown/chmod /data again so because mount is run as root + defaults
    chown system system /data
    chmod 0771 /data

    # Create dump dir and collect dumps.
    # Do this before we mount cache so eventually we can use cache for
    # storing dumps on platforms which do not have a dedicated dump partition.
    # Fake entry for testing
    chmod 0771 /data

replace.sh
Code:
#!/bin/bash
n="1"
pattern="    chmod 0771 /data"
new_pattern="    mkdir /data/system"
awk '$0==patt{which++;if(which==n)$0=$0 RS repl}1' patt="$pattern" repl="$new_pattern" n=$n datadb/data.db >datadb/test.txt

expected output:
Code:
on post-fs-data
    # We chown/chmod /data again so because mount is run as root + defaults
    chown system system /data
    chmod 0771 /data
    mkdir /data/system

    # Create dump dir and collect dumps.
    # Do this before we mount cache so eventually we can use cache for
    # storing dumps on platforms which do not have a dedicated dump partition.
    # Fake entry for testing
    chmod 0771 /data

Works in this way, adding spaces in $pattern. However, these can be inconsistent in data.db...

---------- Post updated at 12:52 PM ---------- Previous update was at 12:46 PM ----------

Quote:
Originally Posted by elixir_sinari
In that case, try:
Code:
awk '$0~"^[ \t]*"patt"[ \t]*$"{which++;if(which==n)$0=$0 RS repl}1' patt="$pattern" repl="$new_pattern" n=$n data.db

No need to provide for spaces/tabs before/after the pattern.
Thank you a lot, you saved my day, and week Smilie
This works perfect

Now, I have another question, what if I want to do the same, but this time replace the pattern whole line by new_pattern and not only insert in a new line after it?

output would be, for n=1

Code:
on post-fs-data
    # We chown/chmod /data again so because mount is run as root + defaults
    chown system system /data
    mkdir /data/system

    # Create dump dir and collect dumps.
    # Do this before we mount cache so eventually we can use cache for
    # storing dumps on platforms which do not have a dedicated dump partition.
    # Fake entry for testing
    chmod 0771 /data

# 10  
Old 09-13-2012
That would need a very small change:
Code:
awk '$0~"^[ \t]*"patt"[ \t]*$"{which++;if(which==n)$0=$0 RS repl}1' patt="$pattern" repl="$new_pattern" n=$n data.db

to
Code:
awk '$0~"^[ \t]*"patt"[ \t]*$"{which++;if(which==n)$0=repl}1' patt="$pattern" repl="$new_pattern" n=$n data.db

Also, I would suggest a small change for performance improvement:
Code:
awk 'which!=n&&$0~"^[ \t]*"patt"[ \t]*$"{which++;if(which==n)$0=repl}1' patt="$pattern" repl="$new_pattern" n=$n data.db

This User Gave Thanks to elixir_sinari For This Post:
Phil3759
# 11  
Old 09-13-2012
Quote:
Originally Posted by elixir_sinari
That would need a very small change:
Code:
awk '$0~"^[ \t]*"patt"[ \t]*$"{which++;if(which==n)$0=$0 RS repl}1' patt="$pattern" repl="$new_pattern" n=$n data.db

to
Code:
awk '$0~"^[ \t]*"patt"[ \t]*$"{which++;if(which==n)$0=repl}1' patt="$pattern" repl="$new_pattern" n=$n data.db

Also, I would suggest a small change for performance improvement:
Code:
awk 'which!=n&&$0~"^[ \t]*"patt"[ \t]*$"{which++;if(which==n)$0=repl}1' patt="$pattern" repl="$new_pattern" n=$n data.db

I am really greatful. Actually, this line was too much for my knowledge
Both the classic and performance ones do work as expected for replace/insert pattern

Now, just for my knowledge (feel free to bypass this, you already helped me a lot):
would you explain the syntax in each part of this line? Smilie
# 12  
Old 09-13-2012
Code:
$0                     --> current input record/line (awk reads one record/line at a time).
~                      --> match operator.
"^[ \t]*"patt"[ \t]*$" --> this becomes ^[ \t]*chmod 0771 /data[ \t]*$ for your pattern. 
                           This means a pattern beginning (^ is the beginning-of-line/record anchor) 
			   with 0 or more (*) of either space and/or tab ([ \t]), followed by the string
			   "chmod 0771 /data" (of course without the quotes), followed by 0 or more of
			   either space and/or tab and then the end-of-line/record ($ is the end of line/record anchor).

which++                --> for such lines, increment the variable "which" by 1 (variables in awk do not need
                           declaration; when referenced for the first time, they are null/zero depending on the context).

if(which==n)           --> check if value of "which" has reached that of "n". If yes (that means the
                           required occurrence), set $0 to the concatenated string of $0, RS (record
			   separator,awk's builtin variable, newline by default) and the replacement string
			   ($0=$0 RS repl).

1                      --> that's a pattern which is always true. So, whether the previous actions changed 
                           $0 or not, print the current line/record.

This User Gave Thanks to elixir_sinari For This Post:
Phil3759
# 13  
Old 09-13-2012
I got it know
Thank you for all the time you spent with my issue

A last (I hope) question

What would be the next 2 commands if I want to insert new_pattern before the pattern

Actual insert command is:
Code:
awk '$0~"^[ \t]*"patt"[ \t]*$"{which++;if(which==n)$0=$0 RS repl}1' patt="$pattern" repl="$new_pattern" n=$n data.db

performance one:
Code:
awk 'which!=n&&$0~"^[ \t]*"patt"[ \t]*$"{which++;if(which==n)$0=$0 RS repl}1' patt="$pattern" repl="$new_pattern" n=$n data.db

# 14  
Old 09-13-2012
Change
Code:
$0=$0 RS repl

to
Code:
$0=repl RS $0

.
This User Gave Thanks to elixir_sinari For This Post:
Phil3759
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