Equivalent to Unix "Less" Command Within R Console

Equivalent to unix less command within R console

There is also page() which displays a representation of an object in a pager, like less.

dat <- data.frame(matrix(rnorm(1000), ncol = 10))
page(dat, method = "print")

Pause print of large object when it fills the screen

Here is a quick and dirty more function:

more <- function(expr, lines=20) {
    out <- capture.output(expr)
    n <- length(out)
    i <- 1
    while( i < n ) {
        j <- 0
        while( j < lines && i <= n ) {
            cat(out[i],"\n")
            j <- j + 1
            i <- i + 1
        }
        if(i<n) readline()
    }
    invisible(out)
}

It will evaluate the expression and print chunks of lines (default to 20, but you can change that). You need to press 'enter' to move on to the next chunk. Only 'Enter' will work, you can't just use the space bar or other keys like other programs and it does not have options for searching, going back, etc.

You can try it with a command like:

more( rnorm(250) )

Here is an expanded version that will quit if you type 'q' or 'Q' (or anything starting with either) then press 'Enter', it will print out the last lines rows of the output if you type 'T' then enter, and if you type a number it will jump to that decile through the output (e.g. typing 5 will jump to half way through, 8 will be 80% of the way through). Anything else and it will continue.

more <- function(expr, lines=20) {
    out <- capture.output(expr)
    n <- length(out)
    i <- 1
    while( i < n ) {
        j <- 0
        while( j < lines && i <= n ) {
            cat(out[i],"\n")
            j <- j + 1
            i <- i + 1
        }
        if(i<n){
            rl <- readline()
            if( grepl('^ *q', rl, ignore.case=TRUE) ) i <- n
            if( grepl('^ *t', rl, ignore.case=TRUE) ) i <- n - lines + 1
            if( grepl('^ *[0-9]', rl) ) i <- as.numeric(rl)/10*n + 1
        }
    }
    invisible(out)
}

Show special characters in Unix while using 'less' Command

less will look in its environment to see if there is a variable named LESS

You can set LESS in one of your ~/.profile (.bash_rc, etc, etc) and then anytime you run less from the comand line, it will find the LESS.

Try adding this

export LESS="-CQaix4"

This is the setup I use, there are some behaviors embedded in that may confuse you, so you can find out about what all of these mean from the help function in less, just tap the 'h' key and nose around, or run less --help.

Edit:

I looked at the help, and noticed there is also an -r option

-r  -R  ....  --raw-control-chars  --RAW-CONTROL-CHARS
                Output "raw" control characters.

I agree that cat may be the most exact match to your stated needs.

cat -vet file | less

Will add '$' at end of each line and convert tab char to visual '^I'.

cat --help
   (edited)
    -e                       equivalent to -vE
    -E, --show-ends          display $ at end of each line
    -t                       equivalent to -vT
    -T, --show-tabs          display TAB characters as ^I
    -v, --show-nonprinting   use ^ and M- notation, except for LFD and TAB

I hope this helps.

Execute less from command-line PHP w/ Scrolling

You could use proc_open to feed input to and get output back from a process via pipes. However, it doesn't seem like less allows for user interaction via pipes as it basically degrades to a cat command. Here's my first (failed) approach:

<?php
$dspec = array(
  0 = array('pipe', 'r'), // pipe to child process's stdin
  1 = array('pipe', 'w'), // pipe from child process's stdout
  2 = array('file', 'error_log', 'a'), // stderr dumped to file
);
// run the external command
$proc = proc_open('less name_of_file_here', $dspec, $pipes, null, null);
if (is_resource($proc)) {
  while (($cmd = readline('')) != 'q') {
    // if the external command expects input, it will get it from us here
    fwrite($pipes[0], $cmd);
    fflush($pipes[0]);
    // we can get the response from the external command here
    echo fread($pipes[1], 1024);
  }
fclose($pipes[0]);
fclose($pipes[1]);
echo proc_close($proc);

I guess for some commands this approach might actually work - and there are some examples in the php manpage for proc_open that might be helpful to look over - but for less, you get the whole file back and no possibility for interaction, maybe for reasons mentioned by Viper_Sb's answer.

...But it seems easy enough to simulate less if that's all you need. For example, you could read the output of the command into an array of lines and feed it in bite-sized chunks:

<?php
$pid = popen('cat name_of_file_here', 'r');
$buf = array();
while ($s = fgets($pid, 1024))
  $buf[] = $s;
pclose($pid);
for ($i = 0; $i < count($buf)/25 && readline('more') != 'q'; $i++) {
  for ($j = 0; $j < 25; $j++) {
    echo array_shift($buf);
  }
}

Equivalent of 'more' or 'less' command in Powershell?

Well... There is "more", which is more or less (...) the same you'd expect from other platforms. Try the following example:

dir -rec | more

Set default help type for the help system in R for Windows

To set the default for help_type option:

> options (help_type = "text")
> getOption ("help_type")
[1] "text"

And, to set the console as the pager instead of R's internal one:

> options (pager = "console")
> getOption ("pager")
[1] "console"

You can even set a particular command as the pager. For example, if you want to use unix's less program provided by cygwin or msys2 or git for Windows:

> options (pager = "less")
> getOption ("pager")
[1] "less"

N.B. Make sure that less is in your path. Otherwise, you would have to provide the full path of it:

> options (pager = "C:\\Program Files\\Git\\usr\\bin\\less.exe")

Where the less program is situated in C:\Program Files\Git\usr\bin\.

See ?options and ?file.show for details.

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