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a - number all lines; t - number lines with printable text only; n - no line numbering; string - number only those lines containing the regular expression defined in the string supplied. The default applied switch is t. nl also supports some command line options.
This displays the first 5 lines of all files starting with foo: head -n 5 foo* Most versions [citation needed] allow omitting n and instead directly specifying the number: -5. GNU head allows negative arguments for the -n option, meaning to print all but the last - argument value counted - lines of each input file.-c bytes --bytes = bytes
Version 1 AT&T UNIX dd: Filesystem Mandatory Convert and copy a file Version 5 AT&T UNIX delta: SCCS Optional (XSI) Make a delta (change) to an SCCS file PWB UNIX df: Filesystem Mandatory Report free disk space Version 1 AT&T UNIX diff: Text processing Mandatory Compare two files; see also cmp Version 5 AT&T UNIX dirname: Filesystem Mandatory
n pops the top of the stack and prints it without a trailing newline. f prints the entire stack with one entry per line. dc also supports arbitrary input and output radices. The i command pops the top of the stack and uses it for the input base. Hex digits must be in upper case to avoid collisions with dc commands and are limited to A-F.
Performing one-liners directly on the Unix command line can be accomplished by using Python's -cmd flag (-c for short), and typically requires the import of one or more modules. Statements are separated using ";" instead of newlines. For example, to print the last field of unix long listing:
tail has two special command line option -f and -F (follow) that allows a file to be monitored. Instead of just displaying the last few lines and exiting, tail displays the lines and then monitors the file. As new lines are added to the file by another process, tail updates the display. This is particularly useful for monitoring log files.
A typical probe might fire when a certain file is opened, or a process is started, or a certain line of code is executed. A probe that fires may analyze the run-time situation by accessing the call stack and context variables and evaluating expressions; it can then print out or log some information, record it in a database, or modify context ...
bc first appeared in Version 6 Unix in 1975. It was written by Lorinda Cherry of Bell Labs as a front end to dc, an arbitrary-precision calculator written by Robert Morris and Cherry. dc performed arbitrary-precision computations specified in reverse Polish notation. bc provided a conventional programming-language interface to the same capability via a simple compiler (a single yacc source ...