177 lines
7.2 KiB
Plaintext
177 lines
7.2 KiB
Plaintext
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'\"
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'\" Copyright (c) 1995-1996 Sun Microsystems, Inc.
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'\"
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'\" See the file "license.terms" for information on usage and redistribution
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'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
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'\"
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.TH filename n 7.5 Tcl "Tcl Built-In Commands"
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.so man.macros
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.BS
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'\" Note: do not modify the .SH NAME line immediately below!
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.SH NAME
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filename \- File name conventions supported by Tcl commands
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.BE
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.SH INTRODUCTION
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.PP
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All Tcl commands and C procedures that take file names as arguments
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expect the file names to be in one of three forms, depending on the
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current platform. On each platform, Tcl supports file names in the
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standard forms(s) for that platform. In addition, on all platforms,
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Tcl supports a Unix-like syntax intended to provide a convenient way
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of constructing simple file names. However, scripts that are intended
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to be portable should not assume a particular form for file names.
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Instead, portable scripts must use the \fBfile split\fR and \fBfile
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join\fR commands to manipulate file names (see the \fBfile\fR manual
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entry for more details).
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.SH "PATH TYPES"
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.PP
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File names are grouped into three general types based on the starting point
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for the path used to specify the file: absolute, relative, and
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volume-relative. Absolute names are completely qualified, giving a path to
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the file relative to a particular volume and the root directory on that
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volume. Relative names are unqualified, giving a path to the file relative
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to the current working directory. Volume-relative names are partially
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qualified, either giving the path relative to the root directory on the
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current volume, or relative to the current directory of the specified
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volume. The \fBfile pathtype\fR command can be used to determine the
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type of a given path.
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.SH "PATH SYNTAX"
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.PP
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The rules for native names depend on the value reported in the Tcl
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\fBplatform\fR element of the \fBtcl_platform\fR array:
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.TP 10
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\fBUnix\fR
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On Unix and Apple MacOS X platforms, Tcl uses path names where the
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components are separated by slashes. Path names may be relative or
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absolute, and file names may contain any character other than slash.
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The file names \fB\&.\fR and \fB\&..\fR are special and refer to the
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current directory and the parent of the current directory respectively.
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Multiple adjacent slash characters are interpreted as a single
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separator. Any number of trailing slash characters at the end of a
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path are simply ignored, so the paths \fBfoo\fR, \fBfoo/\fR and
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\fBfoo//\fR are all identical, and in particular \fBfoo/\fR does not
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necessarily mean a directory is being referred.
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.RS
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.PP
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The following examples illustrate various forms of path
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names:
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.TP 15
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\fB/\fR
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Absolute path to the root directory.
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.TP 15
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\fB/etc/passwd\fR
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Absolute path to the file named \fBpasswd\fR in the directory
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\fBetc\fR in the root directory.
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.TP 15
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\fB\&.\fR
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Relative path to the current directory.
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.TP 15
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\fBfoo\fR
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Relative path to the file \fBfoo\fR in the current directory.
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.TP 15
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\fBfoo/bar\fR
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Relative path to the file \fBbar\fR in the directory \fBfoo\fR in the
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current directory.
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.TP 15
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\fB\&../foo\fR
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Relative path to the file \fBfoo\fR in the directory above the current
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directory.
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.RE
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.TP
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\fBWindows\fR
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On Microsoft Windows platforms, Tcl supports both drive-relative and UNC
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style names. Both \fB/\fR and \fB\e\fR may be used as directory separators
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in either type of name. Drive-relative names consist of an optional drive
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specifier followed by an absolute or relative path. UNC paths follow the
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general form \fB\e\eservername\esharename\epath\efile\fR, but must at
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the very least contain the server and share components, i.e.
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\fB\e\eservername\esharename\fR. In both forms,
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the file names \fB.\fR and \fB..\fR are special and refer to the current
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directory and the parent of the current directory respectively. The
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following examples illustrate various forms of path names:
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.RS
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.TP 15
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\fB\&\e\eHost\eshare/file\fR
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Absolute UNC path to a file called \fBfile\fR in the root directory of
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the export point \fBshare\fR on the host \fBHost\fR. Note that
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repeated use of \fBfile dirname\fR on this path will give
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\fB//Host/share\fR, and will never give just \fB//Host\fR.
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.TP 15
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\fBc:foo\fR
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Volume-relative path to a file \fBfoo\fR in the current directory on drive
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\fBc\fR.
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.TP 15
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\fBc:/foo\fR
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Absolute path to a file \fBfoo\fR in the root directory of drive
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\fBc\fR.
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.TP 15
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\fBfoo\ebar\fR
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Relative path to a file \fBbar\fR in the \fBfoo\fR directory in the current
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directory on the current volume.
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.TP 15
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\fB\&\efoo\fR
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Volume-relative path to a file \fBfoo\fR in the root directory of the current
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volume.
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.TP 15
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\fB\&\e\efoo\fR
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Volume-relative path to a file \fBfoo\fR in the root directory of the current
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volume. This is not a valid UNC path, so the assumption is that the
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extra backslashes are superfluous.
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.RE
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.SH "TILDE SUBSTITUTION"
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.PP
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In addition to the file name rules described above, Tcl also supports
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\fIcsh\fR-style tilde substitution. If a file name starts with a tilde,
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then the file name will be interpreted as if the first element is
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replaced with the location of the home directory for the given user. If
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the tilde is followed immediately by a separator, then the \fB$HOME\fR
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environment variable is substituted. Otherwise the characters between
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the tilde and the next separator are taken as a user name, which is used
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to retrieve the user's home directory for substitution. This works on
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Unix, MacOS X and Windows (except very old releases).
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.PP
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Old Windows platforms do not support tilde substitution when a user name
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follows the tilde. On these platforms, attempts to use a tilde followed
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by a user name will generate an error that the user does not exist when
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Tcl attempts to interpret that part of the path or otherwise access the
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file. The behaviour of these paths when not trying to interpret them is
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the same as on Unix. File names that have a tilde without a user name
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will be correctly substituted using the \fB$HOME\fR environment
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variable, just like for Unix.
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.SH "PORTABILITY ISSUES"
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.PP
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Not all file systems are case sensitive, so scripts should avoid code
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that depends on the case of characters in a file name. In addition,
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the character sets allowed on different devices may differ, so scripts
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should choose file names that do not contain special characters like:
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\fB<>:?"/\e|\fR.
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'\""\" reset emacs highlighting
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The safest approach is to use names consisting of
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alphanumeric characters only. Care should be taken with filenames
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which contain spaces (common on Windows systems) and
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filenames where the backslash is the directory separator (Windows
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native path names).
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.PP
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On Windows platforms there are file and path length restrictions.
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Complete paths or filenames longer than about 260 characters will lead
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to errors in most file operations.
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.PP
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Another Windows peculiarity is that any number of trailing dots
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.QW .
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in filenames are totally ignored, so, for example, attempts to create a
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file or directory with a name
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.QW foo.
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will result in the creation of a file/directory with name
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.QW foo .
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This fact is reflected in the results of \fBfile normalize\fR.
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Furthermore, a file name consisting only of dots
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.QW .........
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or dots with trailing characters
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.QW .....abc
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is illegal.
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.SH "SEE ALSO"
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file(n), glob(n)
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.SH KEYWORDS
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current directory, absolute file name, relative file name,
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volume-relative file name, portability
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