Chapter 4 Input/Output

In this chapter, we will explore commands that will

  • display messages
  • print file contents
  • sort file contents
Command Description
echo Display messages
cat Print contents of a file
head Prints first ten lines of a file by default
tail Prints last ten lines of a file by default
more Open a file for interactive reading, scrolling & searching
less Open a file for interactive reading, scrolling & searching
sort Sort a file in ascending order

4.1 Display Messages

The echo command prints text to the terminal. It can be used for writing or appending messages to a file as well.

Command Description
echo Display messages
echo -n Print message without trailing new line
echo > file Write message to a file
echo >> file Append message to a file
echo -e Enable interpretation of special characters

4.1.2 Redirect Output

What if we want to redirect the output? Instead of printing the text to the terminal, we want to write it to a file. In such cases, use > along with the file name to redirect the output to the file. Keep in mind that > will overwrite files. If you want to append to files instead of overwriting, use >>.

4.4 Tail

The tail command displays the last 10 lines of a file(s) by default. It can be used to display the last few lines or bytes of a file as well.

Command Description
tail Display the last part of a file
tail -n num Show the last num lines of a file
tail -n +num Show all contents of the file starting from num line
tail -c num Show last num bytes of a file
tail -f Keep reading file until Ctrl + C
tail -F Keep reading file until Ctrl + C; even if the file is rotated

4.4.1 Display the last parts of a file

Let us use tail to display the last 10 lines of the file.

## Very Secure Dishes
## Very, Very Secure Dishes
## Supposedly Educational
## Bug in Your Hair
## Sincere Pumpkin Patch
## Another Canoe
## You Stupid Darkness
## Single Candle
## Short Summer
## Kite Eating Tree

4.4.2 Display the last 5 lines of a file

As we did in the previous section, use n to specify the number of lines to be displayed.

## Another Canoe
## You Stupid Darkness
## Single Candle
## Short Summer
## Kite Eating Tree

4.4.3 Display all contents from line 10

We can use tail to display all contents of a file starting from a specific line. In the below example, we display all contents of the file starting from the 10th line using the n option and + prefix while specifying the number of lines.

## Good Sport
## Frisbee Sailing
## Warm Puppy
## Spring Dance
## Sock it to Me
## Pumpkin Helmet
## Smooth Sidewalk
## Full of Ingredients
## World-Famous Astronaut
## Fire Safety
## Wooden Christmas Tree
## Very Secure Dishes
## Very, Very Secure Dishes
## Supposedly Educational
## Bug in Your Hair
## Sincere Pumpkin Patch
## Another Canoe
## You Stupid Darkness
## Single Candle
## Short Summer
## Kite Eating Tree

4.4.4 Display the last 10 bytes of a file

Use the c option to display the last 7 bytes of a file.

##  Tree

4.5 More

The more command displays text, one screen at a time. It opens a file for

  • interactive reading
  • scrolling
  • and searching

Press space to scroll down the page, the forward slash (/) for searching strings, n to go to the next match and q to quit.

Command Description
more Open a file for interactive reading, scrolling & searching
space Page down
/ Search for a string; press n to go the next match
q Quit

4.6 Less

The less command is similar to more but offers more features. It allows the user to scroll up and down, go to the beggining and end of the file, forward and backward search and the ability to go the next and previous match while searching the file.

Command Description
less Open a file for interactive reading, scrolling & searching
space Page down
b Page up
G Go to the end of file
g Go to the start of file
/ Forward search
? Backward search
n Go to next match
N Go to previous match
q Quit

4.7 Sort

The sort command will sort the contents of text file, line by line. Using additional options, we can

  • sort a file in ascending/descending order
  • ignore case while sorting
  • use numeric order for sorting
  • preserve only unique lines while sorting

Using the sort command, the contents can be sorted numerically and alphabetically. By default, the rules for sorting are:

  • lines starting with a number will appear before lines starting with a letter.
  • lines starting with a letter that appears earlier in the alphabet will appear before lines starting with a letter that appears later in the alphabet.
  • lines starting with a lowercase letter will appear before lines starting with the same letter in uppercase.

Using additional options, the rules for sorting can be changed. We list the options in the below table.

Command Description
sort Sort lines of text files
sort -r Sort a file in descending order
sort --ignore-case Ignore case while sorting
sort -n Use numeric order for sorting
sort -u Preserve only unique lines while sorting

4.7.1 Sort

Let us sort the contents of the pkg_names.txt file. It contains names R packages randomly selected from CRAN.

## ASIP
## AdMit
## AnalyzeTS
## AzureStor
## AzureStor
## BIGDAWG
## BIOMASS
## BIOMASS
## BenfordTests
## BinOrdNonNor
## BioCircos
## ClimMobTools
## CombinePValue
## Eagle
## FField
## ICAOD
## MARSS
## MIAmaxent
## MIAmaxent
## MIAmaxent
## MVB
## MVTests
## MaXact
## MaxentVariableSelection
## OptimaRegion
## OxyBS
## PathSelectMP
## PropScrRand
## RJDBC
## RPyGeo
## SCRT
## SMARTp
## SPEDInstabR
## SemiParSampleSel
## SetMethods
## SmallCountRounding
## SpatioTemporal
## SphericalK
## SuppDists
## Survgini
## TIMP
## TSeriesMMA
## VineCopula
## WGScan
## WPKDE
## accept
## accept
## addhaz
## alfr
## aweek
## aweek
## bayesbio
## blink
## breakfast
## cbsem
## corclass
## crsra
## cyclocomp
## dagitty
## disparityfilter
## edfReader
## errorlocate
## expstudies
## fermicatsR
## foretell
## gLRTH
## gazepath
## generalhoslem
## geoknife
## hdnom
## hindexcalculator
## ibd
## interplot
## kfigr
## logNormReg
## ltxsparklines
## lue
## mbir
## mcmcabn
## mev
## mgcViz
## mined
## mlflow
## mongolite
## mongolite
## mvShapiroTest
## odk
## overlapping
## pAnalysis
## pls
## pmdplyr
## poisbinom
## randtests
## redcapAPI
## rgw
## rless
## rsed
## rstudioapi
## solitude
## splithalfr
## sspline
## sybilccFBA
## tailr
## tailr
## tictactoe
## viridisLite
## vqtl
## widyr
## widyr

4.7.2 Descending Order

Using the -r option which stands for --reverse the contents of the file can be sorted in descending/reverse order. Let us now sort the contents of the pkg_names.txt file in reverse order.

## widyr
## widyr
## vqtl
## viridisLite
## tictactoe
## tailr
## tailr
## sybilccFBA
## sspline
## splithalfr
## solitude
## rstudioapi
## rsed
## rless
## rgw
## redcapAPI
## randtests
## poisbinom
## pmdplyr
## pls
## pAnalysis
## overlapping
## odk
## mvShapiroTest
## mongolite
## mongolite
## mlflow
## mined
## mgcViz
## mev
## mcmcabn
## mbir
## lue
## ltxsparklines
## logNormReg
## kfigr
## interplot
## ibd
## hindexcalculator
## hdnom
## geoknife
## generalhoslem
## gazepath
## gLRTH
## foretell
## fermicatsR
## expstudies
## errorlocate
## edfReader
## disparityfilter
## dagitty
## cyclocomp
## crsra
## corclass
## cbsem
## breakfast
## blink
## bayesbio
## aweek
## aweek
## alfr
## addhaz
## accept
## accept
## WPKDE
## WGScan
## VineCopula
## TSeriesMMA
## TIMP
## Survgini
## SuppDists
## SphericalK
## SpatioTemporal
## SmallCountRounding
## SetMethods
## SemiParSampleSel
## SPEDInstabR
## SMARTp
## SCRT
## RPyGeo
## RJDBC
## PropScrRand
## PathSelectMP
## OxyBS
## OptimaRegion
## MaxentVariableSelection
## MaXact
## MVTests
## MVB
## MIAmaxent
## MIAmaxent
## MIAmaxent
## MARSS
## ICAOD
## FField
## Eagle
## CombinePValue
## ClimMobTools
## BioCircos
## BinOrdNonNor
## BenfordTests
## BIOMASS
## BIOMASS
## BIGDAWG
## AzureStor
## AzureStor
## AnalyzeTS
## AdMit
## ASIP

4.7.3 Ignore case

To ignore case while sorting contents, use the --ignore-case option. Time to sort the pkg_names.txt file while ignoring case.

## accept
## accept
## addhaz
## AdMit
## alfr
## AnalyzeTS
## ASIP
## aweek
## aweek
## AzureStor
## AzureStor
## bayesbio
## BenfordTests
## BIGDAWG
## BinOrdNonNor
## BioCircos
## BIOMASS
## BIOMASS
## blink
## breakfast
## cbsem
## ClimMobTools
## CombinePValue
## corclass
## crsra
## cyclocomp
## dagitty
## disparityfilter
## Eagle
## edfReader
## errorlocate
## expstudies
## fermicatsR
## FField
## foretell
## gazepath
## generalhoslem
## geoknife
## gLRTH
## hdnom
## hindexcalculator
## ibd
## ICAOD
## interplot
## kfigr
## logNormReg
## ltxsparklines
## lue
## MARSS
## MaXact
## MaxentVariableSelection
## mbir
## mcmcabn
## mev
## mgcViz
## MIAmaxent
## MIAmaxent
## MIAmaxent
## mined
## mlflow
## mongolite
## mongolite
## MVB
## mvShapiroTest
## MVTests
## odk
## OptimaRegion
## overlapping
## OxyBS
## pAnalysis
## PathSelectMP
## pls
## pmdplyr
## poisbinom
## PropScrRand
## randtests
## redcapAPI
## rgw
## RJDBC
## rless
## RPyGeo
## rsed
## rstudioapi
## SCRT
## SemiParSampleSel
## SetMethods
## SmallCountRounding
## SMARTp
## solitude
## SpatioTemporal
## SPEDInstabR
## SphericalK
## splithalfr
## sspline
## SuppDists
## Survgini
## sybilccFBA
## tailr
## tailr
## tictactoe
## TIMP
## TSeriesMMA
## VineCopula
## viridisLite
## vqtl
## WGScan
## widyr
## widyr
## WPKDE

4.7.4 Numeric Order

To sort numerically, use the -n option which stands for --numeric-sort. In this example, we will use a different file, package_names.txt where the package names are prefixed by random numbers between 1 and 100.

## 1. cyclocomp
## 2. odk
## 3. redcapAPI
## 4. TIMP
## 5. pls
## 6. BinOrdNonNor
## 7. bayesbio
## 8. MVTests
## 9. pAnalysis
## 10. aweek
## 11. hdnom
## 12. ltxsparklines
## 13. MaXact
## 14. RJDBC
## 15. MIAmaxent
## 16. randtests
## 17. ASIP
## 18. gazepath
## 19. mcmcabn
## 20. rless
## 21. corclass
## 22. vqtl
## 23. disparityfilter
## 24. SCRT
## 25. RPyGeo
## 26. blink
## 27. gLRTH
## 28. splithalfr
## 29. sspline
## 29. sspline
## 30. logNormReg
## 31. BIGDAWG
## 31. BIGDAWG
## 32. SPEDInstabR
## 33. tailr
## 33. tailr
## 34. ibd
## 35. fermicatsR
## 36. mlflow
## 37. CombinePValue
## 38. BenfordTests
## 39. mev
## 40. MaxentVariableSelection
## 41. rstudioapi
## 42. OptimaRegion
## 43. accept
## 44. expstudies
## 45. solitude
## 45. solitude
## 46. cbsem
## 47. SMARTp
## 48. geoknife
## 49. SemiParSampleSel
## 50. mbir
## 51. interplot
## 52. ClimMobTools
## 53. MVB
## 54. OxyBS
## 55. hindexcalculator
## 56. MARSS
## 57. generalhoslem
## 58. alfr
## 59. AdMit
## 60. Eagle
## 61. PropScrRand
## 62. lue
## 63. dagitty
## 64. viridisLite
## 65. mined
## 65. mined
## 66. SuppDists
## 67. tictactoe
## 68. AzureStor
## 68. AzureStor
## 69. FField
## 70. rsed
## 70. rsed
## 71. kfigr
## 72. overlapping
## 72. overlapping
## 73. VineCopula
## 74. crsra
## 75. pmdplyr
## 76. errorlocate
## 77. SetMethods
## 78. sybilccFBA
## 79. mvShapiroTest
## 80. SpatioTemporal
## 81. mgcViz
## 82. breakfast
## 83. WPKDE
## 84. BIOMASS
## 85. edfReader
## 86. mongolite
## 87. WGScan
## 88. SphericalK
## 89. foretell
## 90. widyr
## 91. rgw
## 92. BioCircos
## 93. PathSelectMP
## 94. ICAOD
## 95. TSeriesMMA
## 96. poisbinom
## 97. AnalyzeTS
## 98. SmallCountRounding
## 99. Survgini
## 100. addhaz

4.7.5 Preserve Only Unique Lines

The -u option which stands for --unique will preserve only unique lines while sorting the contents of the file. In the below example, we remove all duplicate lines from the pkg_names.txt while sorting.

## ASIP
## AdMit
## AnalyzeTS
## AzureStor
## BIGDAWG
## BIOMASS
## BenfordTests
## BinOrdNonNor
## BioCircos
## ClimMobTools
## CombinePValue
## Eagle
## FField
## ICAOD
## MARSS
## MIAmaxent
## MVB
## MVTests
## MaXact
## MaxentVariableSelection
## OptimaRegion
## OxyBS
## PathSelectMP
## PropScrRand
## RJDBC
## RPyGeo
## SCRT
## SMARTp
## SPEDInstabR
## SemiParSampleSel
## SetMethods
## SmallCountRounding
## SpatioTemporal
## SphericalK
## SuppDists
## Survgini
## TIMP
## TSeriesMMA
## VineCopula
## WGScan
## WPKDE
## accept
## accept
## addhaz
## alfr
## aweek
## bayesbio
## blink
## breakfast
## cbsem
## corclass
## crsra
## cyclocomp
## dagitty
## disparityfilter
## edfReader
## errorlocate
## expstudies
## fermicatsR
## foretell
## gLRTH
## gazepath
## generalhoslem
## geoknife
## hdnom
## hindexcalculator
## ibd
## interplot
## kfigr
## logNormReg
## ltxsparklines
## lue
## mbir
## mcmcabn
## mev
## mgcViz
## mined
## mlflow
## mongolite
## mvShapiroTest
## odk
## overlapping
## pAnalysis
## pls
## pmdplyr
## poisbinom
## randtests
## redcapAPI
## rgw
## rless
## rsed
## rstudioapi
## solitude
## splithalfr
## sspline
## sybilccFBA
## tailr
## tictactoe
## viridisLite
## vqtl
## widyr

4.8 Word Count

wc will print newline, word, and byte counts for file(s). If more than one file is specified, it will also print total line.

4.8.1 Count words, bytes and lines

##  30  73 546 release_names.txt

4.8.2 Count lines in a file

## 30 release_names.txt

4.8.3 Count words in a file

## 73 release_names.txt

4.8.4 Count characters(bytes) in a file

## 546 release_names.txt