Jan Kończak

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os_cp:redirects_pipes [2023/03/22 11:19]
jkonczak 		os_cp:redirects_pipes [2026/03/24 01:04] (current)
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 Name comes from //​con__cat__enate//​. \\ Name comes from //​con__cat__enate//​. \\
 ''​cat''​ numbers lines with the ''​-n''​ switch and outputs non-printable characters ''​cat''​ numbers lines with the ''​-n''​ switch and outputs non-printable characters
-as ''​^//​x//'',​ ''​M-//​x//'',​ … with the ''​-v''​ switch.+as ''​^//​x//'',​ ''​M-//​x//'',​ … with the ''​-v''​ switch((This notation corresponds to keys one would have to press to input the byte. To see all bytes (''​\t''​ and ''​\n''​ is replaced by ''​X''​),​ try: \\ ''​perl -e'​for(0..15){printf"​\t%x_",​$_};​print"​\n";​for$l(0..15){printf"​_%x",​$l;​for$h(0..15){$c=$h<<​4|$l;​$c=88 if $c==9||$c==10;​printf("​\t%c",​$c)}print"​\n"​}'​|cat -v''​)).
  
 ''​**paste** //file_1// [//​file2//​]...''​ reads round-robin one line from each input ''​**paste** //file_1// [//​file2//​]...''​ reads round-robin one line from each input
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 <​small>​ <​small>​
 +''​**join** [-t //​separator//​] [-1 //​fieldNumberInFile1//​] [-2 //​fieldNumberInFile2//​] //file1// //​file2//''​
 +parses two sorted files and prints their lines joined on specified fields. ​
 +
 ''​**fold** [-w //width//] [//​file//​]...''​ outputs input files (or standard input) ''​**fold** [-w //width//] [//​file//​]...''​ outputs input files (or standard input)
 forcing a line break whenever a line would exceed //width// (that defaults to 80). forcing a line break whenever a line would exceed //width// (that defaults to 80).
 \\ \\
 With the ''​-s''​ switch ''​fold''​ breaks lines on spaces (or at //width// if there are no spaces). With the ''​-s''​ switch ''​fold''​ breaks lines on spaces (or at //width// if there are no spaces).
 +
 +''​**column** [-x] [//​file//​]...''​ works just like ''​cat''​ if the longest line in the //file//s (or standard input) would not fit twice within the terminal width. \\ Else, it prints the input in as many columns as fit the terminal, filling column first (or, with ''​-x'',​ rows first).
 +\\
 +''​**column -t** [//​file//​]...''​ does a completely different thing: it detects columns in input (by a separator that defaults to whitespace) and outputs the input as a table.
  
 ''​**od** [-t x1]'',​ ''​**hexdump** [-C]'',​ and ''​**xxd**''​ show binary files. ''​**od** [-t x1]'',​ ''​**hexdump** [-C]'',​ and ''​**xxd**''​ show binary files.
 </​small>​ </​small>​
 +
 +++++ Examples | {{page>​so:​redirects:​cat&​inline}} ++++
  
 ~~Exercise.#​~~ Print any file with ''​cat''​. Print two files at once with ''​cat''​. \\ ~~Exercise.#​~~ Print any file with ''​cat''​. Print two files at once with ''​cat''​. \\
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 ==== Printing text ==== ==== Printing text ====
  
-''​**echo** //​text//''​ outputs //text// followed by a newline ​(unless ​''​-n''​ is specified). \\ +''​**echo** //​text//''​ outputs //text// followed by a newline. \\ 
-The ''​-e''​ switch turns backslash escapes into corresponding characters, e.g., ''​\t''​ +<​small>​ 
-becomes a tab and ''​\n''​ a newline (cf. manual).+The ''​echo'' ​command ​is present in almost any shell of any operating system, 
 +but there is no consensus on how to interpret switches and how to treat 
 +backslashes in the text. 
 +\\ 
 +In Bash, the  ​''​-n''​ switch ​supresses the newline, and ''​-e'' ​turns backslash 
 +escapes into corresponding characters, e.g., ''​\t''​ becomes a tab and ''​\n''​ 
 +a newline (cf. manual). 
 +</​small>​
  
 ''​**printf** //format// [//​arguments//​]...''​ works roughly the same as the ''​printf''​ function in C. ''​**printf** //format// [//​arguments//​]...''​ works roughly the same as the ''​printf''​ function in C.
  
 <​small>​ <​small>​
-''​**figlet** [//​text//​]''​ outputs //text// or the standard input by using ascii-art font. +Here and there, the course materials make use of the following toy commands: 
 +\\ 
 +''​**figlet** [//​text//​]''​ outputs //text// or the standard input by using an ascii-art font. 
 +\\
 ''​**cowsay** [//​text//​]''​ makes a cow say the //text// (or the standard input). ''​**cowsay** [//​text//​]''​ makes a cow say the //text// (or the standard input).
 </​small>​ </​small>​
  
-~~Exercise.#​~~ Try ''​echo -e '​foo\n\nbaz'​ ''​ \\ and ''​echo -e '\n\n one \033[A \033[A two \033[B \033[B \n \033[1;31m red \033[0m'​ ''​+++++ Examples | {{page>​so:​redirects:​echo&​inline}} ++++ 
 + 
 +~~Exercise.#​~~ Try the commands ​''​echo -e '​foo\n\nbaz'​ ''​ \\ and ''​echo -e '\n\n one \033[A \033[A two \033[B \033[B \n \033[1;31m red \033[0m'​ '' ​\\ <​small>​[[https://​en.wikipedia.org/​wiki/​ANSI_escape_code|ANSI escape codes]] are well summarized [[https://​gist.github.com/​fnky/​458719343aabd01cfb17a3a4f7296797|here]]</​small>​
  
 ~~Exercise.#​~~ Try ''​printf "​|%4.2f|%3s|%-20s|\n|%4.2f|%3s|%-20s|\n"​ 3.1428 pi circumference/​radius 9.8 g gravity''​ ~~Exercise.#​~~ Try ''​printf "​|%4.2f|%3s|%-20s|\n|%4.2f|%3s|%-20s|\n"​ 3.1428 pi circumference/​radius 9.8 g gravity''​
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 \\ \\
 With the ''​-w''​ switch, ''​seq''​ makes all number of equal width (e.g., ''​seq -w 8 11''​ outputs 08, 09, 10 and 11). With the ''​-w''​ switch, ''​seq''​ makes all number of equal width (e.g., ''​seq -w 8 11''​ outputs 08, 09, 10 and 11).
 +
 +++++ Examples | {{page>​so:​redirects:​seq&​inline}} ++++
  
 ~~Exercise.#​~~ Generate a sequence of numbers from 1 to 15. ~~Exercise.#​~~ Generate a sequence of numbers from 1 to 15.
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 ~~Exercise.#​~~ Redirect standard output and the standard error of the ''​find /​var/​spool/''​ command to the same file. ~~Exercise.#​~~ Redirect standard output and the standard error of the ''​find /​var/​spool/''​ command to the same file.
 +
 +++++ Examples | {{page>​so:​redirects:​out-en&​inline}} ++++
  
 === Input redirections === === Input redirections ===
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 ~~Exercise.#​~~ Use ''​bc''​ to calculate ''​sqrt(2.0000)''​ in non-interactive mode and redirect its output to a file. ~~Exercise.#​~~ Use ''​bc''​ to calculate ''​sqrt(2.0000)''​ in non-interactive mode and redirect its output to a file.
 +
 +++++ Examples | {{page>​so:​redirects:​in&​inline}} ++++
  
 <​small>​ <​small>​
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 | ''>>''​ | opens //word// for appending and replaces //​file_number//​ with the file | | ''>>''​ | opens //word// for appending and replaces //​file_number//​ with the file |
 | ''<>''​ | opens //word// for reading and writing and replaces //​file_number//​ with the file | | ''<>''​ | opens //word// for reading and writing and replaces //​file_number//​ with the file |
-| ''<<''​ | 1) creates a temporary file \\ 2) reads an input line \\ 3) if the line is //​word//, ​go to step 6 \\ 4) if there are no quotes (a pair of ''"''​ or <​html><​code>'</​code></​html>​) ​in //word//, performs the expansion((E.g.,​ ''​$VAR''​ is substituted with its value, ''​`date`''​ is replaced by output of the date command etc.)) on the line \\ 5) writes ​the line to the temporary file \\ 6) opens the temporary file for reading ​ \\ 7) replace //​file_number//​ with the file \\ The command is run once this is done |+| ''<<''​ | 1) creates a temporary file \\ 2) reads an input line \\ 3) if the line is //​word//, ​goes to step 7 \\ 4) if there are no quotes (a pair of ''"''​ or <​html><​code>'</​code></​html>​) ​enclosing the //word//, performs the expansion((E.g.,​ ''​$VAR''​ is substituted with its value, ''​`date`''​ is replaced by output of the date command etc.)) on the line \\ 5) appends ​the line to the temporary file \\ 6) goes to step 2 \\ 7) opens the temporary file for reading ​ \\ 8) replace //​file_number//​ with the file \\ The command is run once this is done |
 | ''<<​-''​| same as ''<<'',​ but after step 2 adds a step: \\ 2a) erase all leading tab characters (''​\t''​) \\ warning: spaces are not erased | | ''<<​-''​| same as ''<<'',​ but after step 2 adds a step: \\ 2a) erase all leading tab characters (''​\t''​) \\ warning: spaces are not erased |
 | ''<<<''​| warning: this is a Bash extension \\ 1) creates a temporary file \\ 2) writes //word// to it \\ 3) writes a newline to it \\ 4) opens the temporary file for reading ​ \\ 5) replace //​file_number//​ with the file \\ The command is run once this is done | | ''<<<''​| warning: this is a Bash extension \\ 1) creates a temporary file \\ 2) writes //word// to it \\ 3) writes a newline to it \\ 4) opens the temporary file for reading ​ \\ 5) replace //​file_number//​ with the file \\ The command is run once this is done |
-| ''<&''​ | if //word// is a number: duplicates a readable descriptor number //word// to the number //​file_number//​ \\  if //word/// is ''​-'':​ closes a descriptor number //​file_number//​ | +| ''<&''​ | if //word// is a number: duplicates a readable descriptor number //word// to the number //​file_number//​ \\  if //word// is ''​-'':​ closes a descriptor number //​file_number//​ | 
-| ''>&''​ | if //word// is a number: duplicates a writeable descriptor number //word// to the number //​file_number// ​ \\  if //word/// is ''​-'':​ closes a descriptor number //​file_number//​ |+| ''>&''​ | if //word// is a number: duplicates a writeable descriptor number //word// to the number //​file_number// ​ \\  if //word// is ''​-'':​ closes a descriptor number //​file_number//​ |
 | ''&>''​ | warning: this is a Bash extension \\ warning: this does not allow providing //​file_number//​ (in fact, ''&''​ is the file number) \\ opens //word// for writing, truncates it and replaces streams 1 and 2 with the file | | ''&>''​ | warning: this is a Bash extension \\ warning: this does not allow providing //​file_number//​ (in fact, ''&''​ is the file number) \\ opens //word// for writing, truncates it and replaces streams 1 and 2 with the file |
 | ''&>>''​| warning: this is a Bash extension \\ warning: this does not allow providing //​file_number//​ (in fact, ''&''​ is the file number) \\ opens //word// for appending and replaces streams 1 and 2 with the file | | ''&>>''​| warning: this is a Bash extension \\ warning: this does not allow providing //​file_number//​ (in fact, ''&''​ is the file number) \\ opens //word// for appending and replaces streams 1 and 2 with the file |
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 standard output (unless you dare to face the consequences). standard output (unless you dare to face the consequences).
  
-~~Exercise.#​~~ Swap standard ​input with standard output of the+~~Exercise.#​~~ Swap standard ​error with standard output of the
 ''​cat /etc/motd /​etc/​shadow''​ command. Test if you did this correctly by adding ''​cat /etc/motd /​etc/​shadow''​ command. Test if you did this correctly by adding
 ''​|rev''​ at the end (that will put standard output backwards). ''​|rev''​ at the end (that will put standard output backwards).
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 All that is written to a pipe is stored in the main memory (so it never occupies All that is written to a pipe is stored in the main memory (so it never occupies
 disk space, regardless if it is a named pipe) until some program reads it. disk space, regardless if it is a named pipe) until some program reads it.
 +
 +~~Exercise.#​~~ Run ''​echo '​2+2*2'​ ''​. Then, pipe it through ''​bc''​.
  
 ~~Exercise.#​~~ ''​echo''​ some text. Then, echo the text and pipe it through ''​xxd''​. ~~Exercise.#​~~ ''​echo''​ some text. Then, echo the text and pipe it through ''​xxd''​.
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 ~~Exercise.#​~~ Create a named pipe //p//. Redirect input of ''​fold''​ from //p// ~~Exercise.#​~~ Create a named pipe //p//. Redirect input of ''​fold''​ from //p//
 in one terminal, and redirect output of ''​ps -eF''​ to //p// in another terminal. in one terminal, and redirect output of ''​ps -eF''​ to //p// in another terminal.
-\\ Then repeat the commands, running the''​ps''​ before the ''​fold''​.+\\ Then repeat the commands, running the ''​ps''​ before the ''​fold''​.
 </​small>​ </​small>​
 +
 +++++ Examples | {{page>​so:​redirects:​pipes1-en&​inline}} ++++
  
 ===== Filters ===== ===== Filters =====
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 ~~Exercise.#​~~ Run ''​seq 25 > //​file//''​. Then run ''​tail -f //​file//''​ in one ~~Exercise.#​~~ Run ''​seq 25 > //​file//''​. Then run ''​tail -f //​file//''​ in one
 terminal and append (with output redirection) some data to //file//. terminal and append (with output redirection) some data to //file//.
 +
 +++++ Examples | {{page>​so:​pipes_filters:​head_tail&​inline}} ++++
  
 ==== grep ==== ==== grep ====
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 \\ \\
 List all files containing ''​ecdsa''​ in ''​~/​.ssh''​. List all files containing ''​ecdsa''​ in ''​~/​.ssh''​.
 +
 +++++ Examples | {{page>​so:​pipes_filters:​grep&​inline}} ++++
  
 ==== cut ==== ==== cut ====
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 bytes (''​-b //​spec//''​) / fields (''​-f //​spec//''​) in each line. bytes (''​-b //​spec//''​) / fields (''​-f //​spec//''​) in each line.
 \\ \\
-A filed is any number of characters separated by a single-character+A field is any number of characters separated by a single-character
 delimiter (''​-d //​delim//'',​ defaults to tab). delimiter (''​-d //​delim//'',​ defaults to tab).
  
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 ''​egrep '​^[Ee]{2}'​ /​usr/​share/​myspell/​en_US.dic''​ a slash and all that follows ''​egrep '​^[Ee]{2}'​ /​usr/​share/​myspell/​en_US.dic''​ a slash and all that follows
 it. it.
 +
 +++++ Examples | {{page>​so:​pipes_filters:​cut-en&​inline}} ++++
  
 ==== sort ==== ==== sort ====
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 ~~Exercise.#​~~ Sort the file by the second column (alphabetically) and by the third column (numerically). ~~Exercise.#​~~ Sort the file by the second column (alphabetically) and by the third column (numerically).
 </​small>​ </​small>​
 +
 +++++ Examples | {{page>​so:​pipes_filters:​sort&​inline}} ++++
  
 ==== wc, uniq, nl ==== ==== wc, uniq, nl ====
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 \\ \\
 Then pipe it through ''​sort''​ and ''​uniq''​ so that you see how many times each result was hit. Then pipe it through ''​sort''​ and ''​uniq''​ so that you see how many times each result was hit.
 +
 +++++ Examples | {{page>​so:​pipes_filters:​wc_uniq&​inline}} ++++
  
 <​small>​ <​small>​
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   * to squeeze all spaces   * to squeeze all spaces
   * remove all the letters ''​rwx''​   * remove all the letters ''​rwx''​
 +
 +++++ Examples | {{page>​so:​pipes_filters:​tr-en&​inline}} ++++
  
 <​small>​ <​small>​
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 <​small>​ <​small>​
 ~~Exercise.#​~~ Open a PDF file (e.g., ''/​usr/​share/​doc/​packages/​apparmor-docs/​techdoc.pdf''​) with less, with and without -L option. \\ ~~Exercise.#​~~ Open a PDF file (e.g., ''/​usr/​share/​doc/​packages/​apparmor-docs/​techdoc.pdf''​) with less, with and without -L option. \\
-Open a ''​tar''​ archive with less (e.g., ''/​usr/​share/​doc/​packages/​automake/​amhello-1.0.tar.gz''​).+Open a ''​tar''​ archive with less (e.g., ''/​usr/​share/​doc/​packages/​automake/​amhello-1.0.tar.gz''​).\\ 
 +View a directory (e.g., ''/​usr/​include''​) with less.
 </​small>​ </​small>​
  
os_cp/redirects_pipes.1679480358.txt.gz · Last modified: 2023/03/22 11:19 by jkonczak

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