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ReadLine—Wolfram Documentation

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ReadLine["file"]

reads a line of text from a file and returns it as a string.

ReadLine[stream]

reads a line of text from a stream and returns it as a string.

ReadLine[proc]

reads a line of text generated by an external process and returns it as a string.

Details and Options
Details and Options Details and Options
Examples  
Basic Examples  
Scope  
See Also
Related Guides
History
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ReadLine

ReadLine["file"]

reads a line of text from a file and returns it as a string.

ReadLine[stream]

reads a line of text from a stream and returns it as a string.

ReadLine[proc]

reads a line of text generated by an external process and returns it as a string.

Details and Options

  • ReadLine reads until it encounters a newline, either "\n" or "\r\n".
  • ReadLine[File["file"],…] is also supported.
  • ReadLine["file",…] and ReadLine[File["file"],…] will first open "file" for reading if it is not already open. The file will be left open until it is closed by a call to Close.
  • ReadLine["file",…] and ReadLine[File["file"],…] open "file" using OpenRead with BinaryFormatTrue.
  • ReadLine is a blocking function that by default will not return until it has read a complete line of text.
  • With the option setting TimeConstraint->t, ReadLine waits at most t seconds, then returns whatever it has read by that time.
  • If ReadLine is called on a source of content that has already been exhausted, it returns EndOfFile.
  • ReadLine[src] is equivalent to ReadString[src,"\n"|"\r\n"].

Examples

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Basic Examples  (3)

Read the first line of the file "ExampleData/strings":

Wolfram Language code: ReadLine["ExampleData/strings"]

Read the next line:

Wolfram Language code: ReadLine["ExampleData/strings"]

Both outputs are strings:

Wolfram Language code: Head /@ {%, %%}

Close the file:

Wolfram Language code: Close["ExampleData/strings"]

Start the system shell process:

Wolfram Language code: process = StartProcess[$SystemShell]

Read all initial output; depending on the operating system and shell, this can result in an empty string:

Wolfram Language code: ReadString[process, EndOfBuffer];

Write a command into the shell:

Wolfram Language code: WriteLine[process, "echo example"];

Read the command output:

Wolfram Language code: ReadLine[process]

Start the system shell process:

Wolfram Language code: process = StartProcess[$SystemShell]

Read all initial output; depending on the operating system and shell, this can result in an empty string:

Wolfram Language code: ReadString[process, EndOfBuffer];

Write two "echo" commands in the shell, then close it with "exit":

Wolfram Language code: BinaryWrite[process, "echo line 1 echo line 2 exit "];

Read the shell process output:

Wolfram Language code: ReadLine[process]
Wolfram Language code: ReadLine[process]
Wolfram Language code: ReadLine[process]

Scope  (1)

Read the first line of a File object:

Wolfram Language code: ReadLine[File["ExampleData/USConstitution.txt"]]

Close the file:

Wolfram Language code: Close[File["ExampleData/USConstitution.txt"]]
Wolfram Research (2014), ReadLine, Wolfram Language function, https://reference.wolfram.com/language/ref/ReadLine.html (updated 2016).

Text

Wolfram Research (2014), ReadLine, Wolfram Language function, https://reference.wolfram.com/language/ref/ReadLine.html (updated 2016).

CMS

Wolfram Language. 2014. "ReadLine." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2016. https://reference.wolfram.com/language/ref/ReadLine.html.

APA

Wolfram Language. (2014). ReadLine. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/ReadLine.html

BibTeX

@misc{reference.wolfram_2026_readline, author="Wolfram Research", title="{ReadLine}", year="2016", howpublished="\url{https://reference.wolfram.com/language/ref/ReadLine.html}", note=[Accessed: 14-November-2026]}

BibLaTeX

@online{reference.wolfram_2026_readline, organization={Wolfram Research}, title={ReadLine}, year={2016}, url={https://reference.wolfram.com/language/ref/ReadLine.html}, note=[Accessed: 14-November-2026]}