ReadLine

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`ReadLine`

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ReadLine["file"]

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

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ReadLine[stream]

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

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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 BinaryFormatTrue.
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

open allclose all

Basic Examples (3)Summary of the most common use cases

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

In[1]:=1

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https://wolfram.com/xid/0cqz06zo-s9j1dz

Out[1]=1

Read the next line:

In[2]:=2

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https://wolfram.com/xid/0cqz06zo-4f6iso

Out[2]=2

Both outputs are strings:

In[3]:=3

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https://wolfram.com/xid/0cqz06zo-q29fuh

Out[3]=3

Close the file:

In[4]:=4

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https://wolfram.com/xid/0cqz06zo-l8o8tt

Out[4]=4

Start the system shell process:

In[1]:=1

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https://wolfram.com/xid/0cqz06zo-hp8oi3

Out[1]=1

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

In[2]:=2

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https://wolfram.com/xid/0cqz06zo-f7be3i

Write a command into the shell:

In[3]:=3

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https://wolfram.com/xid/0cqz06zo-6j3c93

Read the command output:

In[4]:=4

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https://wolfram.com/xid/0cqz06zo-32mxq4

Out[4]=4

Start the system shell process:

In[1]:=1

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https://wolfram.com/xid/0cqz06zo-1voo50

Out[1]=1

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

In[2]:=2

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https://wolfram.com/xid/0cqz06zo-dtvr3g

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

In[3]:=3

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https://wolfram.com/xid/0cqz06zo-thxrfy

Read the shell process output:

In[4]:=4

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https://wolfram.com/xid/0cqz06zo-8r362x

Out[4]=4

In[5]:=5

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https://wolfram.com/xid/0cqz06zo-g50v84

Out[5]=5

In[6]:=6

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https://wolfram.com/xid/0cqz06zo-efcdg0

Out[6]=6

Scope (1)Survey of the scope of standard use cases

Read the first line of a File object:

In[1]:=1

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https://wolfram.com/xid/0cqz06zo-0gw01t

Out[1]=1

Close the file:

In[2]:=2

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https://wolfram.com/xid/0cqz06zo-cg7rsr

Out[2]=2

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