SUBST(1)

NAME
subst - substitute definitions into file(s)

SYNOPSIS
subst -f substitutions victim ...

DESCRIPTION
Subst makes substitutions into files, in a way that is suitable for customizing software to local conditions. Each victim file is altered according to the contents of the substitutions file.

The substitutions file contains one line per substitution. A line consists of two fields separated by one or more tabs. The first field is the name of the substitution, the second is the value. Neither should contain the character `#', and use of text-editor metacharacters like `&' and `\' is also unwise; the name in particular is best restricted to be alphanumeric. A line starting with `#' is a comment and is ignored.

In the victims, each line on which a substitution is to be made (a target line) must be preceded by a prototype line. The prototype line should be delimited in such a way that it will be taken as a comment by whatever program processes the file later. The prototype line must contain a ``prototype'' of the target line bracketed by `=()<' and `>()='; everything else on the prototype line is ignored. Subst extracts the prototype, changes all instances of substitution names bracketed by `@<' and `>@' to their values, and then replaces the target line with the result.

EXAMPLE

If the substitutions file is

    FIRST	111
    SECOND	222

and the victim file is

    x = 2;
    /* =()<y = @<FIRST>@ + @<SECOND>@;>()= */
    y = 88 + 99;
    z = 5;

then ``subst -f substitutions victim'' changes victim to:

    x = 2;
    /* =()<y = @<FIRST>@ + @<SECOND>@;>()= */
    y = 111 + 222;
    z = 5;

FILES
victimdir/substtmp.new    new version being built
victimdir/substtmp.old    old version during renaming

SEE ALSO
sed(1)

DIAGNOSTICS
Complains and halts if it is unable to create its temporary files or if they already exist.

HISTORY
Written at U of Toronto by Henry Spencer.

BUGS
When creating a file to be substed, it's easy to forget to insert a dummy target line after a prototype line; if you forget, subst ends up deleting whichever line did in fact follow the prototype line.