Shell Scripting removing text before and after strings

Question

I need to shell script a way to get the random unknown junk text out of a text file. I am stuck on how to do this because i don't know what the junk text will say. Basically i need to remove everything before, after, and in between the pieces. I want to keep the text that is inside the pieces.

--Begin file


random unknown junk text

----Begin Piece one ---- 
random important text
----End Piece one ----

random unknown junk text

----Begin Piece two ---- 
random important text
----End Piece two ----

random unknown junk text

----Begin Piece two ---- 
random important text
----End Piece two ----

random unknown junk text


end of file

Dennis Williamson · Accepted Answer · 2011-03-01 19:21:59Z

2

sed -n '/^\(--Begin file\|end of file\)/{p;b}; /^----Begin Piece/{p;:a;n;/^----End Piece/{p;b};p;ba}' inputfile

Explanation:

/^\(--Begin file\|end of file\)/{p;b} - Print the file beginning/ending lines (matches literal text)
/^----Begin Piece/{ - If the line matches the block begin marker
- p - Print it
- :a - label a
- n - Read the next line
- /^----End Piece/{ - If it's the block end marker
  - p - Print it
  - b - Branch to the end to read the next line of input
- } - end if
- p - Print a line that's within the block
- ba - Branch to label a to see if there are more lines in the block
} - end if

edited Mar 1, 2011 at 19:21

answered Mar 1, 2011 at 18:48

Dennis Williamson

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2 Comments

Dennis Williamson Over a year ago

@Matt: sed -n -i ... (with some versions of sed the backup extension argument to -i is mandatory: sed -n -i .bak ...). You can also do sed ... inputfile > temp && mv temp inputfile.

Matt Over a year ago

Awesome that works, thanks for your help. This is the first time i ever had to use sed.

vissi · Accepted Answer · 2011-03-01 18:33:57Z

0

#!/bin/bash
exec 3< file.txt
fl=0
regex='----Begin Piece.+'
regexe='----End Piece.+'
while read <&3
do
    if [ $fl -eq 1 ] && [[ ! "$REPLY" =~ $regexe ]]; then
        echo "$REPLY"
    fi
    if [[ "$REPLY" =~ $regex ]]; then fl=1; fi
    if [[ "$REPLY" =~ $regexe ]]; then fl=0; fi
done
exec 3>&-

edited Mar 1, 2011 at 18:33

answered Mar 1, 2011 at 18:25

vissi

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1 Comment

Dennis Williamson Over a year ago

If you quote the pattern on the right hand side of =~ it ceases to be a regex and is taken literally.

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