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test: extract from POSIX deﬁnition of the test command

NAME test - evaluate expression SYNOPSIS test [expression] [ [expression] ] DESCRIPTION The test utility shall evaluate the expression and indicate the result of the evaluation by its exit status. An exit status of zero indicates that the expression evaluated as true and an exit status of 1 indicates that the expression evaluated as false. In the second form of the utility, which uses “[]” rather than test, the application shall ensure that the square brackets are separate arguments. OPERANDS The application shall ensure that all operators and elements of primaries are presented as separate arguments to the test utility. The following primaries can be used to construct expression: -b file True if file exists and is a block special ﬁle. -c file True if file exists and is a character special ﬁle. -d file True if file exists and is a directory. -e file True if file exists. -f file True if file exists and is a regular ﬁle. -g file True if file exists and its set-group-ID ﬂag is set. -h file True if file exists and is a symbolic link. -L file True if file exists and is a symbolic link. -n string True if the length of string is non-zero. -p file True if file is a fifo. -r file True if file exists and is readable. True shall indicate that permission to read from file will be granted, as deﬁned in File Read, Write, and Creation. -S file True if file exists and is a socket. -s file True if file exists and has a size greater than zero. -t file descriptor True if the ﬁle whose ﬁle descriptor number is file descriptor is open and is associated with a terminal. -u file True if file exists and its set-user-ID ﬂag is set. -w file True if file exists and is writable. True shall indicate that permission to write from file will be granted, as deﬁned in File Read, Write, and Creation. -x file True if file exists and is executable. True shall indicate that permission to execute file will be granted, as deﬁned in File Read, Write, and Creation. If file is a directory, true shall indicate that permission to search file will be granted. -z string True if the length of string string is zero. string True if the string string is not the null string.
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s1 = s2 True if the strings s1 and s2 are identical. s1 != s2 True if the strings s1 and s2 are not identical. n1 -eq n2 True if the integers n1 and n2 are algebraically equal. n1 -ne n2 True if the integers n1 and n2 are not algebraically equal. n1 -gt n2 True if the integer n1 is algebraically greater than the integer n2. n1 -ge n2 True if the integer n1 is algebraically greater than or equal to the integer n2. n1 -lt n2 True if the integer n1 is algebraically less than the integer n2. n1 -le n2 True if the integer n1 is algebraically less than or equal to the integer n2. expression1 -a expression2 True if both expression1 and expression2 are true. The -a binary primary is left associative. It has a higher precedence than -o. expression1 -o expression2 True if either expression1 or expression2 is true. The -o binary primary is left associative.

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Numeric File Permissions: an Excerpt from the GNU Documentation

File permissions are stored internally as 16 bit integers. As an alternative to giving a symbolic mode, you can give an octal (base 8) number that corresponds to the internal representation of the new mode. This number is always interpreted in octal; you do not have to add a leading 0, as you do in C. Mode 0055 is the same as mode 55. A numeric mode is usually shorter than the corresponding symbolic mode, but it is limited in that it can not take into account a ﬁle’s previous permissions; it can only set them absolutely. The permissions granted to the user, to other users in the ﬁle’s group, and to other users not in the ﬁle’s group are each stored as three bits, which are represented as one octal digit. The three special permissions are also each stored as one bit, and they are as a group represented as another octal digit. Here is how the bits are arranged in the 16 bit integer, starting with the lowest valued bit: Value in Mode 1 2 4 10 20 40 100 200 400 1000 2000 4000 Corresponding Permission Other users not in the ﬁle’s group: Execute Write Read Other users in the ﬁle’s group: Execute Write Read The ﬁle’s owner: Execute Write Read Special permissions: Save text image on swap device Set group ID on execution Set user ID on execution

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For example, numeric mode 4755 corresponds to symbolic mode ‘u=rwxs,go=rx’, and numeric mode 664 corresponds to symbolic mode ‘ug=rw,o=r’. Numeric mode 0 corresponds to symbolic mode ‘ugo=’.

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• • • •

sed: an Excerpt from Lecture Notes
sed provides many facilities for editing ﬁles sed reads from standard input and writes to standard output The substitute command, s///, is the most important The syntax (using sed as an editor of standard input), is: $ sed ’s/original /replacement /’ • Example: replace the ﬁrst instance of Windows with Linux on each line of the input: sed ’s/Windows/Linux/’ • Example: replace all instances of Windows with Linux on each line of the input: sed ’s/Windows/Linux/g’

sed—the Stream Editor

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Syntax of Some POSIX Commands

find [ path ...] [ expression ]
find searches the directory tree rooted at each path by evaluating expression from left to right. The ﬁrst argument that begins with ‘-’, ‘(’, ‘)’, ‘,’, or ‘!’ is taken to be the beginning of the expression ; any arguments before it are path s to search, and any arguments after it are the rest of the expression . Expressions: The expression is made up of options (which aﬀect overall operation rather than the processing of a speciﬁc ﬁle, and always return true), tests (which return a true or false value), and actions (which have side eﬀects and return a true or false value), all separated by operators. -and is assumed where the operator is omitted. If the expression contains no actions, -print is performed on all ﬁles for which the expression is true. Tests: -name pattern Base of ﬁle name (the path with the leading directories removed) matches shell pattern pattern . Actions: -exec command ; Execute command ; true if 0 status is returned. All following arguments to ﬁnd are taken to be arguments to the command until an argument consisting of ‘;’ is encountered. The string ‘{}’ is replaced by the current ﬁle name being processed. Both of these constructions might need to be escaped (with a ‘\’) or quoted to protect them from expansion by the shell. The command is executed in the starting directory. -print True; print the full ﬁle name on the standard output, followed by a newline.

xargs [ options ] [ command

[ initial-arguments ]]

xargs reads arguments from the standard input, delimited by blanks (which can be protected with double or single quotes or a backslash) or newlines, and executes the command (default is /bin/echo) one or more times with any initial-arguments followed by arguments read from standard input. Blank lines on the standard input are ignored.
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Options: --replace, -i Replace occurences of {} in the initial arguments with names read from standard input. Also, unquoted blanks do not terminate arguments.

egrep [ options ] pattern [ ﬁle ...] grep [ options ] pattern [ ﬁle ...]
grep searches the named input ﬁle s (or standard input if no ﬁles are named, or the ﬁle name - is given) for lines containing a match to the given pattern . By default, grep prints the matching lines. Options: -E, --extended-regexp Interpret pattern as an extended regular expression. egrep is the same as grep -E. -c, --count Suppress normal output; instead print a count of matching lines for each input ﬁle. With the -v, --invert-match option (see below), count non-matching lines. -v, --invert-match Invert the sense of matching, to select non-matching lines.

sort [ option ...] [ ﬁle ...]
Write sorted concatenation of all ﬁle (s) to standard output. Options: -b, --ignore-leading-blanks ignore leading blanks -f, --ignore-case fold lower case to upper case characters -k pos1 [, pos2 ], --key= pos1 [, pos2 ] start a key at pos1 , end it at pos2 (column numbers start with 1) -r, --reverse reverse the result of comparisons -n, --numeric-sort compare according to string numerical value -t sep , --field-separator= sep

diff [ options ] from-ﬁle

to-ﬁle

In the simplest case, diﬀ compares the contents of the two ﬁles from-ﬁle and to-ﬁle . -u Use the uniﬁed output format.

cut [ option ...] [ ﬁle ...]
Print selected parts of lines from each FILE to standard output. -b, --bytes= list output only these bytes -c, --characters= list output only these characters -d delim , -delimiter= delim use delim instead of TAB for ﬁeld delimiter
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-f list , --fields= list output only these ﬁelds; also print any line that contains no delimiter character Use one, and only one of -b, -c or -f. Each list is made up of one range, or many ranges separated by commas. Each range is one of: N N th byte, character or ﬁeld, counted from 1 N- from N th byte, character or ﬁeld, to end of line N -M from N th to M th (included) byte, character or ﬁeld -M from ﬁrst to M th (included) byte, character or ﬁeld

file [ option ...] ﬁle ...
Identify the type of a ﬁle by examining the beginning of the ﬁle, and comparing with patterns in the “magic” ﬁle /usr/share/file/magic. Options: -b Do not prepend ﬁlenames to output lines (brief mode).

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awk: an Excerpt from Lecture notes
• awk is a complete programming language • Mostly used for one-line solutions to problems of extracting columns of data from text, and processing it What Does awk Do? • • • • • awk reads ﬁle(s) or standard input one line at a time, and automatically splits the line into ﬁelds, and calls them $1, $2,. . . , $NF NF is equal to the number of ﬁelds the line was split into $0 contains the whole line awk has an option -F that allows you to select another pattern as the ﬁeld separator ◦ Normally awk splits columns by white space • To execute code after all lines are processed, create an END block. awk Examples • Print the sizes of all ﬁles in current directory: $ ls -l | awk ’{print $5}’ • Add the sizes of all ﬁles in current directory and print the size: $ ls -l | awk ’{sum += $5} END{print sum}’ • Print only the permissions, user, group and ﬁle names of ﬁles in current directory: $ ls -l | awk ’{print $1, $3, $4, $NF}’

Basic awk

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Extract from manual page for crontab ﬁle format

A crontab ﬁle contains instructions to the cron(8) daemon of the general form: “run this command at this time on this date”. Each user has their own crontab, and commands in any given crontab will be executed as the user who owns the crontab. Blank lines and leading spaces and tabs are ignored. Lines whose ﬁrst non-space character is a pound-sign (#) are comments, and are ignored. Note that comments are not allowed on the same line as cron commands, since they will be taken to be part of the command. cron(8) examines cron entries once every minute. The time and date ﬁelds are: ﬁeld minute hour day of month month day of week allowed values 0–59 0–23 1–31 1–12 (or names, see below) 0–7 (0 or 7 is Sun, or use names)

A ﬁeld may be an asterisk (*), which always stands for “ﬁrst-last”. Ranges of numbers are allowed. Ranges are two numbers separated with a hyphen. The speciﬁed range is inclusive. For example, 8-11 for an “hours” entry speciﬁes execution at hours 8, 9, 10 and 11. Lists are allowed. A list is a set of numbers (or ranges) separated by commas. Examples: “1,2,5,9”, “0-4,8-12”. Step values can be used in conjunction with ranges. Following a range with “/ number ” speciﬁes skips of the number ’s value through the range. For example, “0-23/2” can be used in the hours ﬁeld to specify command execution every other hour (the alternative in the V7 standard is “0,2,4,6,8,10,12,14,16,18,20,22”). Steps are also permitted after an asterisk, so if you want to say “every two hours”, just use “*/2”. Names can also be used for the “month” and “day of week” ﬁelds. Use the ﬁrst three letters of the particular day or month (case doesn’t matter). Ranges or lists of names are not allowed. The “sixth” ﬁeld (the rest of the line) speciﬁes the command to be run. The entire command portion of the line, up to a newline or % character, will be executed by /bin/sh or by the shell speciﬁed in the SHELL variable of the cronﬁle. Percent-signs (%) in the command, unless escaped with backslash (\), will be changed into newline characters, and all data after the ﬁrst % will be sent to the command as standard input. Note: The day of a command’s execution can be speciﬁed by two ﬁelds day of month, and day of week. If both ﬁelds are restricted (ie, aren’t *), the command will be run when either ﬁeld matches the current time. For example, “30 4 1,15 * 5” would cause a command to be run at 4.30 am on the 1st and 15th of each month, plus every Friday. EXAMPLE CRON FILE # run 50* # run 15 14 five minutes after midnight, every day ** $HOME/bin/daily.job >> $HOME/tmp/out 2>&1 at 2:15pm on the first of every month 1** $HOME/bin/monthly
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# run at 10 pm on weekdays, annoy Joe 0 22 * * 1-5 mail -s "It’s 10pm" joe%Joe,%%Where are your kids?% 23 0-23/2 * * * echo "run 23 minutes after midn, 2am, 4am ..., everyday" 5 4 * * sun echo "run at 5 after 4 every sunday"

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Examples of using rsync over SSH

In these examples, the options -avz mean: -a, --archive is a simple way of saying you want to copy recursively (i.e., all subdirectories), and preserve all permissions, ownerships and time stamps. -v, --verbose increase the amount of information given; one -v will print the name of each ﬁle as it is transferred, and a brief summary at the end. -z, --compress Compress the data sent to the destination. -e ssh tells rsync to transfer the data over secure shell (ssh). To transfer content of directory, but not the directory itself, from /usr/src/ on the local machine to the directory /usr/local/sources on host ictlab $ rsync -avz -e ssh /usr/src/ ictlab:/usr/local/sources So for example, a ﬁle /usr/src/file.c on the local machine will be transferred to the name /usr/ local/sources/file.c on the host ictlab. Note the trailing slash on the source directory name. To transfer the directory /usr/src itself, from the local machine to the directory /usr/local/ sources on host ictlab $ rsync -avz -e ssh /usr/src ictlab:/usr/local/sources So for example, a ﬁle /usr/src/file.c on the local machine will be transferred to the name /usr/ local/src/sources/file.c on the host ictlab. Note there is no trailing slash on the source directory name.

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Help Output for some bash Builtin Commands

trap [ arg ] [ signal spec ...]
The command arg is to be read and executed when the shell receives signal(s) signal spec . If arg is absent all speciﬁed signals are reset to their original values. If arg is the null string each signal spec is ignored by the shell and by the commands it invokes. If a signal spec is EXIT (0) the command arg is executed on exit from the shell. If a signal spec is DEBUG, arg is executed after every command. If arg is ‘-p’ then the trap commands associated with each signal spec are displayed. If no arguments are supplied or if only ‘-p’ is given, trap prints the list of commands associated with each signal number. Each signal spec is either a signal name in <signal.h> or a signal number. Note that a signal can be sent to the shell with “kill -signal $$”.

jobs [-lnprs] [ jobspec ...]
Lists the active jobs. The -l option lists process ids in addition to the normal information; the -p option lists process ids only. If -n is given, only processes that have changed status since the last notiﬁcation are printed. jobspec restricts output to that job. The -r and -s options restrict output to running and stopped jobs only, respectively. Without options, the status of all active jobs is printed.
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fg [ jobspec ]
Place jobspec in the foreground, and make it the current job. If jobspec is not present, the shell’s notion of the current job is used.

bg [ jobspec ]
Place jobspec in the background, as if it had been started with ‘&’. If jobspec is not present, the shell’s notion of the current job is used.

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Regular Expression Metacharacters
Quote the next metacharacter Match the beginning of the line Match any character (except newline) Match the end of the line (or before newline at the end) Alternation Grouping, and captures so that it can be used as a backreference Character class Negated character class Match 0 or more times Match 1 or more times Match 1 or 0 times Match exactly n times Match at least n times Match at least n but not more than m times

\ ^ . $ | (...) [...] [^...] + ? {n} {n,} {n,m}

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