os_cp:redirects_pipes
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os_cp:redirects_pipes [2023/03/31 15:22] jkonczak [cut] |
os_cp:redirects_pipes [2026/03/24 14:33] (current) jkonczak [more, less] |
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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). | ||
| Line 43: | Line 46: | ||
| ==== 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). | + | ''echo'' 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> | ||
| Line 57: | Line 69: | ||
| ++++ Examples | {{page>so:redirects:echo&inline}} ++++ | ++++ Examples | {{page>so:redirects:echo&inline}} ++++ | ||
| - | ~~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' '' \\ <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 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'' | ||
| Line 170: | Line 182: | ||
| ~~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 === | ||
| Line 198: | Line 212: | ||
| ~~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> | ||
| Line 220: | Line 236: | ||
| | ''>>'' | 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 | | ||
| Line 330: | Line 346: | ||
| ~~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 ===== | ||
| Line 360: | Line 378: | ||
| ~~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 ==== | ||
| Line 371: | Line 391: | ||
| <small> | <small> | ||
| The ''grep'' program accepts several regular expression grammars. | The ''grep'' program accepts several regular expression grammars. | ||
| - | POSIX [[https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html|specifies]] | + | POSIX [[https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/V1_chap09.html|specifies]] |
| basic (default for ''grep'') and extended regular expressions (selectable with | basic (default for ''grep'') and extended regular expressions (selectable with | ||
| ''egrep'' or ''grep -E'' ). See manual for your implementation of ''grep'' for | ''egrep'' or ''grep -E'' ). See manual for your implementation of ''grep'' for | ||
| Line 406: | Line 426: | ||
| \\ | \\ | ||
| List all files containing ''ecdsa'' in ''~/.ssh''. | List all files containing ''ecdsa'' in ''~/.ssh''. | ||
| + | |||
| + | ++++ Examples | {{page>so:pipes_filters:grep&inline}} ++++ | ||
| ==== cut ==== | ==== cut ==== | ||
| Line 427: | Line 449: | ||
| ''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 ==== | ||
| Line 471: | Line 495: | ||
| ~~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 ==== | ||
| Line 503: | Line 529: | ||
| \\ | \\ | ||
| 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> | ||
| Line 537: | Line 565: | ||
| * 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> | ||
| Line 579: | Line 609: | ||
| not human-readable file format. | not human-readable file format. | ||
| \\ | \\ | ||
| - | ''[[https://github.com/wofr06/lesspipe|lesspipe]]'' is the leading implementation | + | ''[[https://lesspipe.org|lesspipe]]'' is the leading implementation |
| of this feature. | of this feature. | ||
| </small> | </small> | ||
os_cp/redirects_pipes.1680268962.txt.gz · Last modified: 2023/03/31 15:22 by jkonczak
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