how to download a file using just bash and nothing else (no curl, wget, perl, etc.)

Question

I have a minimal headless *nix which does not have any command line utilities for downloading files (e.g. no curl, wget, etc). I only have bash.

How can I download a file?

Ideally, I would like a solution that would work across a wide range of *nix.

Answer 1

If you have bash 2.04 or above with the /dev/tcp pseudo-device enabled, you can download a file from bash itself.

Paste the following code directly into a bash shell (you don't need to save the code into a file for executing):

function __wget() {
    : ${DEBUG:=0}
    local URL=$1
    local tag="Connection: close"
    local mark=0

    if [ -z "${URL}" ]; then
        printf "Usage: %s \"URL\" [e.g.: %s http://www.google.com/]" \
               "${FUNCNAME[0]}" "${FUNCNAME[0]}"
        return 1;
    fi
    read proto server path <<<$(echo ${URL//// })
    DOC=/${path// //}
    HOST=${server//:*}
    PORT=${server//*:}
    [[ x"${HOST}" == x"${PORT}" ]] && PORT=80
    [[ $DEBUG -eq 1 ]] && echo "HOST=$HOST"
    [[ $DEBUG -eq 1 ]] && echo "PORT=$PORT"
    [[ $DEBUG -eq 1 ]] && echo "DOC =$DOC"

    exec 3<>/dev/tcp/${HOST}/$PORT
    echo -en "GET ${DOC} HTTP/1.1\r\nHost: ${HOST}\r\n${tag}\r\n\r\n" >&3
    while read line; do
        [[ $mark -eq 1 ]] && echo $line
        if [[ "${line}" =~ "${tag}" ]]; then
            mark=1
        fi
    done <&3
    exec 3>&-
}

Then you can execute it as from the shell as follows:

__wget http://example.iana.org/

Source: Moreaki's answer upgrading and installing packages through the cygwin command line?

Update: as mentioned in the comment, the approach outlined above is simplistic:

• the read will trashes backslashes and leading whitespace.
• Bash can't deal with NUL bytes very nicely so binary files are out.
• unquoted $line will glob.

Answer 2

Use lynx.

It is pretty common for most of Unix/Linux.

lynx -dump http://www.google.com

-dump: dump the first file to stdout and exit

man lynx

Or netcat:

/usr/bin/printf 'GET / \n' | nc www.google.com 80

Or telnet:

(echo 'GET /'; echo ""; sleep 1; ) | telnet www.google.com 80

Answer 3

Adapted from Chris Snow's answer.  This can also handle binary files.

function __curl() {
  read -r proto server path <<<"$(printf '%s' "${1//// }")"
  if [ "$proto" != "http:" ]; then
    printf >&2 "sorry, %s supports only http\n" "${FUNCNAME[0]}"
    return 1
  fi
  DOC=/${path// //}
  HOST=${server//:*}
  PORT=${server//*:}
  [ "${HOST}" = "${PORT}" ] && PORT=80

  exec 3<>"/dev/tcp/${HOST}/$PORT"
  printf 'GET %s HTTP/1.0\r\nHost: %s\r\n\r\n' "${DOC}" "${HOST}" >&3
  (while read -r line; do
   [ "$line" = $'\r' ] && break
  done && cat) <&3
  exec 3>&-
}

• I break && cat to get out of read.
• I use HTTP 1.0 so there's no need to wait for/send a connection:close.

You can test binary files like this:

$ __curl http://www.google.com/favicon.ico >   mine.ico
$ curl   http://www.google.com/favicon.ico > theirs.ico
$ md5sum mine.ico theirs.ico
f3418a443e7d841097c714d69ec4bcb8  mine.ico
f3418a443e7d841097c714d69ec4bcb8  theirs.ico

Answer 4

Taking the "just Bash and nothing else" strictly, here's one adaptation of earlier answers (@Chris's, @131's) that does not call any external utilities (not even standard ones) but also works with binary files:

#!/bin/bash
download() {
  read proto server path <<< "${1//"/"/ }"
  DOC=/${path// //}
  HOST=${server//:*}
  PORT=${server//*:}
  [[ x"${HOST}" == x"${PORT}" ]] && PORT=80

  exec 3<>/dev/tcp/${HOST}/$PORT

  # send request
  echo -en "GET ${DOC} HTTP/1.0\r\nHost: ${HOST}\r\n\r\n" >&3

  # read the header, it ends in a empty line (just CRLF)
  while IFS= read -r line ; do 
      [[ "$line" == $'\r' ]] && break
  done <&3

  # read the data
  nul='\0'
  while IFS= read -d '' -r x || { nul=""; [ -n "$x" ]; }; do 
      printf "%s$nul" "$x"
  done <&3
  exec 3>&-
}

Use with download http://path/to/file > file.

We deal with NUL bytes with read -d ''. It reads until a NUL byte, and returns true if it found one, false if it didn't. Bash can't handle NUL bytes in strings, so when read returns with true, we add the NUL byte manually when printing, and when it returns false, we know there are no NUL bytes any more, and this should be the last piece of data.

Tested with Bash 4.4 on files with NULs in the middle, and ending in zero, one or two NULs, and also with the wget and curl binaries from Debian. The 373 kB wget binary took about 5.7 seconds to download. A speed of about 65 kB/s or a bit more than 512 kb/s.

In comparison, @131's cat-solution finishes in less than 0.1 s, or almost a hundred times faster. Not very surprising, really.

This is obviously silly, since without using external utilities, there's not much we can do with the downloaded file, not even make it executable.

Answer 5

Use uploading instead, via SSH from your local machine

A "minimal headless *nix" box means you probably SSH into it. So you can also use SSH to upload to it. Which is functionally equivalent to downloading (of software packages etc.) except when you want a download command to include in a script on your headless server of course.

As shown in this answer, you would execute the following on your local machine to place a file on your remote headless server:

wget -O - http://example.com/file.zip | ssh user@host 'cat >/path/to/file.zip'

Faster uploading via SSH from a third machine

The disadvantage of the above solution compared to downloading is lower transfer speed, since the connection with your local machine usually has much less bandwidth than the connection between your headless server and other servers.

To solve that, you can of course execute the above command on another server with decent bandwidth. To make that more comfortable (avoiding a manual login on the third machine), here is a command to execute on your local machine.

To be secure, copy & paste that command including the leading space character ' '. See the explanations below for the reason.

 ssh user@intermediate-host "sshpass -f <(printf '%s\n' yourpassword) \
   ssh -T -e none \
     -o StrictHostKeyChecking=no \
     < <(wget -O - http://example.com/input-file.zip) \
     user@target-host \
     'cat >/path/to/output-file.zip' \
"

Explanations:

• The command will ssh to your third machine intermediate-host, start downloading a file to there via wget, and start uploading it to target-host via SSH. Downloading and uploading use the bandwidth of your intermediate-host and happen at the same time (due to Bash pipe equivalents), so progress will be fast.

• When using this, you have to replace the two server logins (user@*-host), the target host password (yourpassword), the download URL (http://example.com/…) and the output path on your target host (/path/to/output-file.zip) with appropriate own values.

• For the -T -e none SSH options when using it to transfer files, see these detailed explanations.

• This command is meant for cases where you can't use SSH's public key authentication mechanism – it still happens with some shared hosting providers, notably Host Europe. To still automate the process, we rely on sshpass to be able to supply the password in the command. It requires sshpass to be installed on your intermediate host (sudo apt-get install sshpass under Ubuntu).

• We try to use sshpass in a secure way, but it will still not be as secure as the SSH pubkey mechanism (says man sshpass). In particular, we supply the SSH password not as a command line argument but via a file, which is replaced by bash process substitution to make sure it never exists on disk. The printf is a bash built-in, making sure this part of the code does not pop up as a separate command in ps output as that would expose the password [source]. I think that this use of sshpass is just as secure as the sshpass -d<file-descriptor> variant recommended in man sshpass, because bash maps it internally to such a /dev/fd/* file descriptor anyway. And that without using a temp file [source]. But no guarantees, maybe I overlooked something.

• Again to make the sshpass usage safe, we need to prevent the command from being recorded to the bash history on your local machine. For that, the whole command is prepended with one space character, which has this effect.

• The -o StrictHostKeyChecking=no part prevents the command from failing in case it never connected to the target host. (Normally, SSH would then wait for user input to confirm the connection attempt. We make it proceed anyway, to not have an indefinitely hanging command on the intermediate host.)

• sshpass expects a ssh or scp command as its last argument. So we have to rewrite the typical wget -O - … | ssh … command into a form without a bash pipe, as explained here.

Answer 6

Based on Chris Snow's script.  I made some improvements:

• http scheme check (it only supports http)
• http response validation (response status line check, and split header and body by '\r\n' line, not 'Connection: close' which is not true sometimes)
• failed on non-200 code (it's important to download files on the internet)

Here is the code:

function __wget() {
    : "${DEBUG:=0}"
    local URL=$1
    local tag="Connection: close"

    if [ -z "${URL}" ]; then
        printf "Usage: %s \"URL\" [e.g., %s http://www.google.com/]" \
               "${FUNCNAME[0]}" "${FUNCNAME[0]}"
        return 1;
    fi  
    read -r proto server path <<< "$(printf '%s' "${URL//// }")"
    local SCHEME=${proto//:*}
    local PATH=/${path// //} 
    local HOST=${server//:*}
    local PORT=${server//*:}
    if [[ "$SCHEME" != "http" ]]; then
        printf "sorry, %s only supports http\n" "${FUNCNAME[0]}"
        return 1
    fi  
    [[ "${HOST}" == "${PORT}" ]] && PORT=80
    [[ "$DEBUG" -eq 1 ]] && echo "SCHEME=$SCHEME" >&2
    [[ "$DEBUG" -eq 1 ]] && echo "HOST=$HOST"     >&2
    [[ "$DEBUG" -eq 1 ]] && echo "PORT=$PORT"     >&2
    [[ "$DEBUG" -eq 1 ]] && echo "PATH=$PATH"     >&2

    if ! exec 3<>"/dev/tcp/${HOST}/$PORT"; then
        return "$?"
    fi  
    
    if ! echo -en "GET ${PATH} HTTP/1.1\r\nHost: ${HOST}\r\n${tag}\r\n\r\n" >&3 ; then
        return "$?"
    fi  
    # 0: at begin, before reading http response
    # 1: reading header
    # 2: reading body
    local state=0
    local num=0
    local code=0
    while read -r line; do
        num=$((num + 1))
        # check http code
        if [ "$state" -eq 0 ]; then
            if [ "$num" -eq 1 ]; then
                if [[ $line =~ ^HTTP/1\.[01][[:space:]]([0-9]{3}).*$ ]]; then
                    code="${BASH_REMATCH[1]}"
                    if [[ "$code" != "200" ]]; then
                        printf "failed to wget '%s', code is not 200 (%s)\n" \
                               "$URL" "$code"
                        exec 3>&-
                        return 1
                    fi
                    state=1
                else
                    printf "invalid http response from '%s'" "$URL"
                    exec 3>&-
                    return 1
                fi
            fi
        elif [ "$state" -eq 1 ]; then
            if [[ "$line" == $'\r' ]]; then
                # found "\r\n"
                state=2
            fi
        elif [ "$state" -eq 2 ]; then
            # redirect body to stdout
            # TODO: any way to pipe data directly to stdout?
            echo "$line"
        fi
    done <&3
    exec 3>&-
}

Answer 7

If you have this package libwww-perl

You can simply use:

/usr/bin/GET

Answer 8

If you have python2:

/usr/bin/python2.7 -c "import sys; import urllib2; exec('try: response = urllib2.urlopen(\'http://localhost:8080/ping\');\nexcept Exception as e: sys.exit(1)')"