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Full Discussion: Replace value of a variable in a file through script using sed
Top Forums Shell Programming and Scripting Replace value of a variable in a file through script using sed Post 302668085 by alister on Sunday 8th of July 2012 02:01:05 PM
Old 07-08-2012
Quote:
Originally Posted by rituparna_gupta
Code:
sed "s/${b}/15/g" abc.txt

Have tried various forms of sed (with single quotes, without quotes, with -e option, etc) but getting the same error with all:
Code:
sed: -e expression #1, char 0: no previous regular expression

You are getting that error because the shell variable, ${b}, is unset or null. After its expansion, the sed command becomes s//15/g. In sed, an empty regular expression is equivalent to the most recently used regular expression. Since there is none, you get that error.

Regards,
Alister
 

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LEARN ABOUT NETBSD

script

SCRIPT(1)						    BSD General Commands Manual 						 SCRIPT(1)

NAME

     script -- make typescript of terminal session

SYNOPSIS

     script [-adfpqr] [-c command] [file]

DESCRIPTION

     script makes a typescript of everything printed on your terminal.	It is useful for students who need a hardcopy record of an interactive
     session as proof of an assignment, as the typescript file can be printed out later with lpr(1).

     If the argument file is given, script saves all dialogue in file.	If no file name is given, the typescript is saved in the file typescript.

     Option:

     -a      Append the output to file or typescript, retaining the prior contents.

     -c command
	     Run the named command instead of the shell.  Useful for capturing the output of a program that behaves differently when associated
	     with a tty.

     -d      When playing back a session with the -p flag, don't sleep between records when playing back a timestamped session.

     -f      Flush output after each write.  This is useful for watching the script output in real time.

     -p      Play back a session recorded with the -r flag in real time.

     -q      Be quiet, and don't output started and ended lines.

     -r      Record a session with input, output, and timestamping.

     The script ends when the forked shell exits (a control-D to exit the Bourne shell (sh(1)), and exit, logout or control-d (if ignoreeof is not
     set) for the C-shell, csh(1)).

     Certain interactive commands, such as vi(1), create garbage in the typescript file.  script works best with commands that do not manipulate
     the screen, the results are meant to emulate a hardcopy terminal.

ENVIRONMENT

     The following environment variable is used by script:

     SHELL  If the variable SHELL exists, the shell forked by script will be that shell.  If SHELL is not set, the Bourne shell is assumed.  (Most
	    shells set this variable automatically).

SEE ALSO

     csh(1) (for the history mechanism).

HISTORY

     The script command appeared in 3.0BSD.

BUGS

     script places everything in the log file, including linefeeds and backspaces.  This is not what the naive user expects.

BSD
								 October 17, 2009							       BSD
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