# Tcl_TildeSubst - replace tilde with home directory in a file name

## SYNOPSIS

    #include <tcl.h>

    char *
    Tcl_TildeSubst(interp, name, bufferPtr)

## ARGUMENTS

Tcl_Interp *interp (in)
  Interpreter in which to report an error, if any.

char *name (in)
  File name, which may start with a ``~''.

Tcl_DString *bufferPtr ()
  If needed, this dynamic string is used to store the new file name. At the time of the call it should be uninitialized or empty. The caller must eventually call Tcl_DStringFree to free up anything stored here.

## DESCRIPTION

This utility procedure does tilde substitution. If name doesn't start with a ``~'' character, then the procedure returns name. If name does start with a tilde, then Tcl_TildeSubst returns a new string identical to name except that the first element of name is replaced with the location of the home directory for the given user. The substitution is carried out in the same way that it would be done by csh. If the tilde is followed immediately by a slash, then the $HOME environment variable is substituted. Otherwise the characters between the tilde and the next slash are taken as a user name, which is looked up in the password file; the user's home directory is retrieved from the password file and substituted.

If Tcl_TildeSubst has to do tilde substitution then it uses the dynamic string at *bufferPtr to hold the new string it generates. After Tcl_TildeSubst returns a non-NULL result, the caller must eventually invoke Tcl_DStringFree to free up any information placed in *bufferPtr. The caller need not know whether or not Tcl_TildeSubst actually used the string; Tcl_TildeSubst initializes *bufferPtr even if it doesn't use it, so the call to Tcl_DStringFree will be safe in either case.

If an error occurs (e.g. because there was no user by the given name) then NULL is returned and an error message will be left at interp->result. When an error occurs, Tcl_TildeSubst frees the dynamic string itself so that the caller need not call Tcl_DStringFree.

The caller is responsible for making sure that interp->result has its default empty value when Tcl_TildeSubst is invoked.

## KEYWORDS

file name, home directory, tilde, user