while list-1; do list-2; done
until list-1; do list-2; done
The while command continuously executes the list list-2 as long as the last command in the list
list-1 returns an exit status of zero. The until command is identical to the while command,
except that the test is negated; list-2 is executed as long as the last command in list-1 returns
a non-zero exit status. The exit status of the while and until commands is the exit status of the
last command executed in list-2, or zero if none was executed.
|
do nothing, successfully
|
(list) list is executed in a subshell environment (see COMMAND EXECUTION ENVIRONMENT below). Variable
assignments and builtin commands that affect the shell's environment do not remain in effect after
the command completes. The return status is the exit status of list.
|
print or set the system date and time
|
Pipelines
A pipeline is a sequence of one or more commands separated by one of the control operators | or |&. The
format for a pipeline is:
[time [-p]] [ ! ] command [ [|⎪|&] command2 ... ]
The standard output of command is connected via a pipe to the standard input of command2. This
connection is performed before any redirections specified by the command (see REDIRECTION below). If |&
is used, the standard error of command is connected to command2's standard input through the pipe; it is
shorthand for 2>&1 |. This implicit redirection of the standard error is performed after any
redirections specified by the command.
The return status of a pipeline is the exit status of the last command, unless the pipefail option is
enabled. If pipefail is enabled, the pipeline's return status is the value of the last (rightmost)
command to exit with a non-zero status, or zero if all commands exit successfully. If the reserved word
! precedes a pipeline, the exit status of that pipeline is the logical negation of the exit status as
described above. The shell waits for all commands in the pipeline to terminate before returning a value.
If the time reserved word precedes a pipeline, the elapsed as well as user and system time consumed by
its execution are reported when the pipeline terminates. The -p option changes the output format to that
specified by POSIX. When the shell is in posix mode, it does not recognize time as a reserved word if
the next token begins with a `-'. The TIMEFORMAT variable may be set to a format string that specifies
how the timing information should be displayed; see the description of TIMEFORMAT under Shell Variables
below.
When the shell is in posix mode, time may be followed by a newline. In this case, the shell displays the
total user and system time consumed by the shell and its children. The TIMEFORMAT variable may be used
to specify the format of the time information.
Each command in a pipeline is executed as a separate process (i.e., in a subshell).
|
translate or delete characters
|
-d, --delete
delete characters in SET1, do not translate
|
tr [OPTION]... SET1 [SET2]
Translate, squeeze, and/or delete characters from standard input, writing to standard output.
SETs are specified as strings of characters. Most represent themselves. Interpreted sequences are:
\NNN character with octal value NNN (1 to 3 octal digits)
\\ backslash
\a audible BEL
\b backspace
\f form feed
\n new line
\r return
\t horizontal tab
\v vertical tab
CHAR1-CHAR2
all characters from CHAR1 to CHAR2 in ascending order
[CHAR*]
in SET2, copies of CHAR until length of SET1
[CHAR*REPEAT]
REPEAT copies of CHAR, REPEAT octal if starting with 0
[:alnum:]
all letters and digits
[:alpha:]
all letters
[:blank:]
all horizontal whitespace
[:cntrl:]
all control characters
[:digit:]
all digits
[:graph:]
all printable characters, not including space
[:lower:]
all lower case letters
[:print:]
all printable characters, including space
[:punct:]
all punctuation characters
[:space:]
all horizontal or vertical whitespace
[:upper:]
all upper case letters
[:xdigit:]
all hexadecimal digits
[=CHAR=]
all characters which are equivalent to CHAR
|
print sensors information
|
print lines matching a pattern
|
-i, --ignore-case
Ignore case distinctions in both the PATTERN and the input files. (-i is specified by POSIX.)
|
grep searches the named input FILEs (or standard input if no files are named, or if a single hyphen-minus
(-) is given as file name) for lines containing a match to the given PATTERN. By default, grep prints
the matching lines.
|
delay for a specified amount of time
|
read from standard input and write to standard output and files
|
-a, --append
append to the given FILEs, do not overwrite
|
Copy standard input to each FILE, and also to standard output.
If a FILE is -, copy again to standard output.
|