Append a print statement to every line in a file with the previous line as output

Question

In troubleshooting a reboot crash I need to print every line in a file to an output console. What I want to do is run a linux command line or script to take each line in a file, and put a print statement after it containing the line, so for example:

while x<100
    x=x+1
end while

would become

while x<100
print "while x<100"
    x=x+1
    print "x=x+1"
end while
print "end while"

even better would be if the print statements could include the line number:

while x<100
print "Line 50: while x<100"
    x=x+1
    print "Line 52:x=x+1"
end while
print "Line 54: end while"

The idea here is to find the last line in the script that executes as that will be the line that probably caused the device to reboot. Currently I do this manually, and it is rather time consuming to add all those lines.

I'm aware of the existence of SED and AWK but have never used them, I do use ex/vi/grep/ls/wc fairly often to sort things out in text files though and have experience with basic shell scripting.

EDIT: Note that none of the code in my question is a shell script. I'm looking for help with creating a shell script or a command line to process a file so that each line in the file is followed by a print statement containing the previous line.

It's important to know what language your code IS in, to know how to escape the data in the print statement when your line of code already contains quotes. — Russell Reed, Dec 21 '14 at 02:47
reading your purpose with the answer, to me it seems that you try to instrument your script instead of properly debugging it. an approach likes [this](http://stackoverflow.com/questions/21190771/how-to-properly-debug-a-bash-script) to use `set -xv` or `extdebug`, looks more feasible. — lp_, Dec 21 '14 at 10:43

αғsнιη · Accepted Answer · 2014-12-23T11:46:50.633

2

awk '{printf("%s\nprint \"Line %s : %s\"\n",$0,++NR, $0)}' infile > outfile

while x<100
print "Line 2 : while x<100"
    x=x+1
print "Line 4 :     x=x+1"
end while
print "Line 6 : end while"

$0 is content of each line, NR is line/record number.

for the lines that already have quotes and print statements, use the below modified awk command:

awk '{printf("%s\nprint \"Line %s : ",$0,++NR)} {gsub(/\"/,"\\\"");printf $0"\"\n"}' infile > outfile

edited Dec 23 '14 at 11:46

answered Dec 21 '14 at 08:51

αғsнιη

2,627
2
25
38

Thanks, your answer exposed some flaws in my thinking as well, now I need to figure out how to handle lines that already have quotes and print statements, possibly just adding a " in front of the : might work – alphablender Dec 22 '14 at 20:24
1

@alphablender Updated answer for handling the lines if already have quotes. – αғsнιη Dec 23 '14 at 11:47

randomusername · Answer 2 · 2014-12-23T04:59:05.217

1

Well, a basic Bash shell script would be

while read -r line
do
  echo "$line"
  printf "print \"%q\"\n" "$line"
done

This uses only bash builtins and is meant to be placed in a script file (typing it in at the terminal may confuse the read command). It currently takes input from stdin, but a redirection operator such as command < file.txt will fix that.

Also note the use of the %q format specifier in the call to printf, it makes sure that the resulting output can be passed back into the shell to get the same text out of it.

edited Dec 23 '14 at 04:59

answered Dec 21 '14 at 04:15

randomusername

7,927
23
50

the output isn't clean and appears to be in reverse order, and lines are smushed together, also, every output line has a print statement on it, not every other line – alphablender Dec 22 '14 at 20:17
@alphablender see my edit, I added a newline character to the ``printf`` function to fix it. – randomusername Dec 23 '14 at 04:01
You also need to add double quotes to `echo "$line"` because otherwise any metacharacters in `line` are going to be interpreted by the shell (redirection, wildcard, variable expansion ... havoc). Similarly you should use `read -r` to provide, eherm, less "useful" semantics for `read`. – tripleee Dec 23 '14 at 04:56
@tripleee true, I've added those in – randomusername Dec 23 '14 at 04:59
As I said in my first comment, the output isn't clean, by that I mean, it is full of backslashes in between words: txtfer=createobject("rourltransfer") print "txtfer=createobject$\"rourltransfer\"$" Pasting into Stack Overflow comment box I lose some of the backslashes, so you can't see how bad it is unfortunately, but it is quite severe – alphablender Dec 27 '14 at 03:10

Append a print statement to every line in a file with the previous line as output

2 Answers2