# fix print command

## Syntax

    fix ID group-ID print N string keyword value ...

- ID, group-ID are documented in fix command
- print = style name of this fix command
- N = print every N steps
- string = text string to print with optional variable names
- zero or more keyword/value pairs may be appended
- keyword = file or append or screen or title

    file value = filename
    append value = filename
    screen value = yes or no
    title value = string
      string =  text to print as 1st line of output file

## Examples

    fix extra all print 100 "Coords of marker atom = $x $y $z"
    fix extra all print 100 "Coords of marker atom = $x $y $z" file coord.txt

## Description

Print a text string every N steps during a simulation run. This can be used for diagnostic purposes or as a debugging tool to monitor some quantity during a run. The text string must be a single argument, so it should be enclosed in double quotes if it is more than one word. If it contains variables it must be enclosed in double quotes to insure they are not evaluated when the input script line is read, but will instead be evaluated each time the string is printed.

See the variable command for a description of equal style variables which are the most useful ones to use with the fix print command, since they are evaluated afresh each timestep that the fix print line is output. Equal-style variables calculate formulas involving mathematical operations, atom properties, group properties, thermodynamic properties, global values calculated by a compute or fix, or references to other variables.

If the file or append keyword is used, a filename is specified to which the output generated by this fix will be written. If file is used, then the filename is overwritten if it already exists. If append is used, then the filename is appended to if it already exists, or created if it does not exist.

If the screen keyword is used, output by this fix to the screen and logfile can be turned on or off as desired.

The title keyword allow specification of the string that will be printed as the first line of the output file, assuming the file keyword was used. By default, the title line is as follows:

    # Fix print output for fix ID

where ID is replaced with the fix-ID. if title = ‘none’, then no title line will be printed

## Restart, fix_modify, output, run start/stop, minimize info

No information about this fix is written to binary restart files. None of the fix_modify options are relevant to this fix. No global or per-atom quantities are stored by this fix for access by various output commands. No parameter of this fix can be used with the start/stop keywords of the run command. This fix is not invoked during `energy minimization`.

## Restrictions

> none

## Related commands

variable, print

## Default

The option defaults are no file output, screen = yes, and title string as described above.