r_install: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/libexec/TeXmacs/bin/r_install - from package: TeXmacs

You may install the required package with command yum install {package}
Error in other languages:
r_install: bevel nie gevind nie
r_install: comandă negăsită
r_install: comando não encontrado
r_install: commande introuvable
r_install: command not found
r_install: käsku ei ole
r_install: không tìm thấy lệnh
r_install: komanda nerasta
r_install: Kommando nicht gefunden.
r_install: kommandot finns inte
r_install: komut yok
r_install: nie znaleziono polecenia
r_install: níor aimsíodh an t-ordú
r_install: no se encontró la orden
r_install: no s'ha trobat l'ordre
r_install: opdracht niet gevonden
r_install: parancs nem található
r_install: perintah tidak ditemukan
r_install: príkaz nenájdený
r_install: příkaz nenalezen
r_install: команда не найдена
r_install: командата не е открита
r_install: 命令找不到
r_install: コマンドが見つかりません