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Editing files in shell programing
07-13-2005
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CAT(1) BSD General Commands Manual CAT(1) NAME
cat -- concatenate and print files SYNOPSIS
cat [-beflnstuv] [-] [file ...] DESCRIPTION
The cat utility reads files sequentially, writing them to the standard output. The file operands are processed in command line order. A single dash represents the standard input, and may appear multiple times in the file list. The word ``concatenate'' is just a verbose synonym for ``catenate''. The options are as follows: -b Implies the -n option but doesn't number blank lines. -e Implies the -v option, and displays a dollar sign ('$') at the end of each line as well. -f Only attempt to display regular files. -l Set an exclusive advisory lock on the standard output file descriptor. This lock is set using fcntl(2) with the F_SETLKW command. If the output file is already locked, cat will block until the lock is acquired. -n Number the output lines, starting at 1. -s Squeeze multiple adjacent empty lines, causing the output to be single spaced. -t Implies the -v option, and displays tab characters as '^I' as well. -u The -u option guarantees that the output is unbuffered. -v Displays non-printing characters so they are visible. Control characters print as '^X' for control-X; the delete character (octal 0177) prints as '^?'. Non-ascii characters (with the high bit set) are printed as 'M-' (for meta) followed by the character for the low 7 bits. EXIT STATUS
The cat utility exits 0 on success, and >0 if an error occurs. EXAMPLES
The command: cat file1 will print the contents of file1 to the standard output. The command: cat file1 file2 > file3 will sequentially print the contents of file1 and file2 to the file file3, truncating file3 if it already exists. See the manual page for your shell (i.e., sh(1)) for more information on redirection. The command: cat file1 - file2 - file3 will print the contents of file1, print data it receives from the standard input until it receives an EOF ('^D') character, print the con- tents of file2, read and output contents of the standard input again, then finally output the contents of file3. Note that if the standard input referred to a file, the second dash on the command-line would have no effect, since the entire contents of the file would have already been read and printed by cat when it encountered the first '-' operand. SEE ALSO
head(1), hexdump(1), lpr(1), more(1), pr(1), tail(1), view(1), vis(1), fcntl(2) Rob Pike, "UNIX Style, or cat -v Considered Harmful", USENIX Summer Conference Proceedings, 1983. STANDARDS
The cat utility is expected to conform to the IEEE Std 1003.2-1992 (``POSIX.2'') specification. The flags [-belnstv] are extensions to the specification. HISTORY
A cat utility appeared in Version 1 AT&T UNIX. Dennis Ritchie designed and wrote the first man page. It appears to have been cat(1). BUGS
Because of the shell language mechanism used to perform output redirection, the command ``cat file1 file2 > file1'' will cause the original data in file1 to be destroyed! This is performed by the shell before cat is run. BSD
September 23, 2006 BSD